Grimoire stops running after a few snapshots in FuzzBench

I'm trying to run a FuzzBench experiment on the mruby target after applying https://github.com/google/fuzzbench/pull/2048 and https://github.com/AFLplusplus/libafl_fuzzbench/pull/13. After applying these patches, the experiment starts successfully, and I get reasonable results from the first few snapshots (the corpus directories contain Ruby-like test cases, and the coverage increases).

However, after several snapshots, it seems that nothing happens anymore. I receive some heartbeat messages in the log, but the corpus directories remain empty, and the coverage stops increasing. This issue occurred in all 5 out of 5 trials after 30 to 60 minutes of fuzzing.

My guess is that there's an issue with the crash, timeout, or restart handling of the SUT (even though it appears to be similar to other grammar-aware fuzzer implementations like Nautilus, Gramatron, and token-level fuzzers, which work fine). Alternatively, it could be a problem with the mutator implementation. Unfortunately, I'm not familiar with Rust or the Grimoire implementation.

Has anyone faced a similar issue or have any idea what might be happening here?