I did some debugging on the C side, using 'rr':

LD_LIBRARY_PATH=.libs ../meta/uninstalled-env rr record ./.libs/guile --fresh-auto-compile -l ../crash.scm

it leads to a segfault, as expected.  According to #39954, which looks
similar, 'frame-local-ref' returns (SCM)0x0.  So I tried some reverse debugging:

rr replay guile-3
break scm_frame_local_ref
reverse-continue
reverse-continue

I noticed "repr" was STACK_ITEM_SCM, and item->as_scm was set to 0x07
(which is invalid).  On another run, it was set to 0x09 (also invalid?).
I modified scm_frame_local_ref a bit so it ignores these 0x07 and 0x09
and treats them like SCM_EOF_VAL instead.  That allows printing the backtrace,
though I don't see those #<eof> appearing in the output.

Would someone know what's going on here?

Greetings,
Maxime