ASSERT 32-bit apps on Ubuntu 20: signal.c:5474 syscall_signal || safe_is_in_fcache()

This shows up in many, many 32-bit Dr. Memory tests where I've been attempting to upgrade GA CI there to Ubuntu 20.04 in https://github.com/DynamoRIO/drmemory/pull/2418

<Application /home/runner/work/drmemory/drmemory/build_drmemory-dbg-32/tests/fuzz_corpus (30809).  Internal Error: DynamoRIO debug check failure: /home/runner/work/drmemory/drmemory/dynamorio/core/unix/signal.c:5474 syscall_signal || safe_is_in_fcache(dcontext, pc, (byte *)sc->SC_XSP)
2021-09-06T17:30:03.3305727Z 74: (Error occurred @1807 frags in tid 30809)

There are 32-bit signal tests failing for plain DR on Ubuntu 20.04 as well in PR #5072 -- but I haven't seen this assert be reported there. @abhinav92003 could you confirm you haven't see this assert? It seems weird that it would only show up in Dr. Memory tests. You would expect similar underlying DR issues and not two different sets of signal problems.