openfortivpn hangs to the point it can't be interrupted, can only be killed

[smktpd]

I run sudo openfortivpn ... --persistent=15 --otp "$(...)".
The server is configured so that it doesn't ask to specify TOTP more frequently than once every 3h.
The interactive log looks like this:

INFO:   Connected to gateway.
INFO:   Authenticated.
INFO:   Remote gateway has allocated a VPN.
...
INFO:   Tunnel is up and running.
INFO:   Cancelling threads...
INFO:   Cleanup, joining threads...
INFO:   Setting ppp0 interface down.
INFO:   Restoring routes...
delete host ${pub_ip_of_vpn_server}: gateway 192.168.88.1
${date} : Hangup (SIGHUP)
${date} : Modem hangup
${date} : Connection terminated.
${date} : LCP close (User request).
${date} : Connect time 24.1 minutes.
${date} : Sent 435481 bytes, received 5043662 bytes.
ERROR:  pppd: The link was terminated by the modem hanging up.
INFO:   Terminated pppd.
INFO:   Closed connection to gateway.
INFO:   Logged out.
INFO:   Connected to gateway.
ERROR:  Could not authenticate to gateway. Please check the password, client certificate, etc.
INFO:   Closed connection to gateway.
INFO:   Logged out.
INFO:   Connected to gateway.
ERROR:  Could not authenticate to gateway. Please check the password, client certificate, etc.
... # the last 4 lines get repeated like 50 times
^C^C^C # I hit Ctrl+c to send interrupt to no avail

only kill helps and since I run sudo openfortivpn I have 2 processes - 1 owned by my user (sudo process) and the other owned by root (openfortivpn process), so I have to sudo kill -s KILL the latter.

I'm on ARM-based device with macos Sonoma 14.6 (23G80) running openfortivpn installed from brew, tried versions 1.20.5 and 1.22.1 (latest available).