[frontend] ImageSlowLoading is not working

[klucsik]

Bug Report

The ImageSlowLoad problem pattern is not working.

Symptom

When the flag switched on, the requests to /images/products/SOMEJPG doesn't contain the envoy fault header.

Reproduce

spin up the demo, set the imageSlowLoad to 5sec or 10sec, refresh frontend -> the images will load instantly

Additional Context

My suspicion is #1670, but I don't know yet why it would broke this.
In 1.11.0 the feature is working well. In 1.11.1, the bug is present.
The bulk of the relevant code is in src/frontend/components/ProductCard/ProductCard.tsx
The problem pattern is added in #1515. #1571 is also relevant.