diff --git a/CarpetX/src/interpolate.cxx b/CarpetX/src/interpolate.cxx
index de484f68d..6df61fc1c 100644
--- a/CarpetX/src/interpolate.cxx
+++ b/CarpetX/src/interpolate.cxx
@@ -39,12 +39,34 @@ template <typename T, int order, int centering> struct interpolator {
                                              (centering & 0b001) != 0};
 
   const GridDescBase &grid;
+#ifdef CCTK_DEBUG
+  const int gi;
+#endif
   const int vi;
+#ifdef CCTK_DEBUG
+  const int patch;
+  const int level;
+#endif
   const amrex::Array4<const T> &vars;
   const vect<int, dim> &derivs;
   // Allow outer boundaries as interpolation sources
   const bool allow_boundaries;
 
+  interpolator(const GridDescBase &grid, CCTK_ATTRIBUTE_UNUSED const int gi,
+               const int vi, const int patch, const int level,
+               const amrex::Array4<const T> &vars, const vect<int, dim> &derivs,
+               const bool allow_boundaries)
+      : grid(grid),
+#ifdef CCTK_DEBUG
+        gi(gi),
+#endif
+        vi(vi),
+#ifdef CCTK_DEBUG
+        patch(patch), level(level),
+#endif
+        vars(vars), derivs(derivs), allow_boundaries(allow_boundaries) {
+  }
+
   static constexpr T eps() {
     using std::pow;
     return pow(std::numeric_limits<T>::epsilon(), T(3) / 4);
@@ -65,8 +87,9 @@ template <typename T, int order, int centering> struct interpolator {
 #ifdef CCTK_DEBUG
     using std::isfinite;
     if (!(isfinite(val))) {
-      std::cerr << "!isfinite i=" << i << " di=" << di << " val=" << val
-                << "\n";
+      std::cerr << "!isfinite gi=" << gi
+                << " groupname=" << CCTK_FullGroupName(gi) << " vi=" << vi
+                << " i=" << i << " di=" << di << " val=" << val << "\n";
       for (int c = -1; c <= +1; ++c)
         for (int b = -1; b <= +1; ++b)
           for (int a = -1; a <= +1; ++a)
@@ -504,7 +527,10 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
     const int level = 0;
     const auto &restrict leveldata = patchdata.leveldata.at(level);
     const amrex::MFIter mfi(*leveldata.fab);
-    assert(mfi.isValid());
+    // The mfi can be invalid if the number of processes does not evenly divide
+    // the number of blocks
+    if (!mfi.isValid())
+      continue;
     ParticleTile *const particle_tile = &containers.at(patch).GetParticles(
         level)[make_pair(mfi.index(), mfi.LocalTileIndex())];
 
@@ -544,8 +570,8 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
              ++pti) {
           const auto &particles = pti.GetArrayOfStructs();
           const int component = MFPointer(pti).index();
-          CCTK_VINFO("patch %d level %d component %d old_nparticles: %zu",
-                     patch, lev, component, particles.size());
+          // CCTK_VINFO("patch %d level %d component %d old_nparticles: %zu",
+          //            patch, lev, component, particles.size());
           for (const auto &particle : particles) {
             oldids.insert(particle.id());
             // CCTK_VINFO("    id=%d proc=%d pos=[%g,%g,%g]  locals=[%g,%g,%g] "
@@ -578,8 +604,8 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
              ++pti) {
           const int component = MFPointer(pti).index();
           const auto &particles = pti.GetArrayOfStructs();
-          CCTK_VINFO("patch %d level %d component %d new_nparticles: %zu",
-                     patch, lev, component, particles.size());
+          // CCTK_VINFO("patch %d level %d component %d new_nparticles: %zu",
+          //            patch, lev, component, particles.size());
           for (const auto &particle : particles) {
             newids.insert(particle.id());
             // CCTK_VINFO("    id=%d proc=%d pos=[%g,%g,%g]  locals=[%g,%g,%g] "
@@ -600,10 +626,12 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
     if (new_nparticles != old_nparticles) {
       for (const auto oldid : oldids)
         if (!newids.count(oldid))
-          CCTK_VINFO("old id %d not present in new ids", oldid);
+          CCTK_VWARN(CCTK_WARN_ALERT, "old id %d not present in new ids",
+                     oldid);
       for (const auto newid : newids)
         if (!oldids.count(newid))
-          CCTK_VINFO("new id %d not present in old ids", newid);
+          CCTK_VWARN(CCTK_WARN_ALERT, "new id %d not present in old ids",
+                     newid);
       CCTK_VERROR(
           "We lost interpolation points on patch %d. Before redistributing: "
           "%zu particles, after redistributing: %zu particles",
@@ -637,6 +665,7 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
     const int patch = patchdata.patch;
     for (const auto &leveldata : patchdata.leveldata) {
       const int level = leveldata.level;
+
       // TODO: use OpenMP
       for (amrex::ParIter<3, 2> pti(containers.at(patch), level); pti.isValid();
            ++pti) {
@@ -683,31 +712,36 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
             switch (interpolation_order) {
             case 0: {
               const interpolator<CCTK_REAL, 0, 0b000> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 1: {
               const interpolator<CCTK_REAL, 1, 0b000> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 2: {
               const interpolator<CCTK_REAL, 2, 0b000> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 3: {
               const interpolator<CCTK_REAL, 3, 0b000> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 4: {
               const interpolator<CCTK_REAL, 4, 0b000> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
@@ -726,31 +760,36 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
             switch (interpolation_order) {
             case 0: {
               const interpolator<CCTK_REAL, 0, 0b111> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 1: {
               const interpolator<CCTK_REAL, 1, 0b111> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 2: {
               const interpolator<CCTK_REAL, 2, 0b111> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 3: {
               const interpolator<CCTK_REAL, 3, 0b111> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
             case 4: {
               const interpolator<CCTK_REAL, 4, 0b111> interp{
-                  grid, vi, vars, derivs, bool(allow_boundaries)};
+                  grid,  gi,   vi,     patch,
+                  level, vars, derivs, bool(allow_boundaries)};
               interp.interpolate3d(particles, varresult);
               break;
             }
@@ -850,6 +889,7 @@ extern "C" void CarpetX_Interpolate(const CCTK_POINTER_TO_CONST cctkGH_,
   // Set result
   CCTK_REAL *const restrict *const restrict resultptrs =
       static_cast<CCTK_REAL *const *>(resultptrs_);
+  assert(int(recvbuf.size()) == (nvars + 1) * npoints);
   for (int n = 0; n < npoints; ++n) {
     const int offset = (nvars + 1) * n;
     const int idx = int(recvbuf.at(offset));