guest account = chris
if 'chris' belongs to only ONE group a core dump on start up is
very likely. I believe the core dump happens in the qsort function
which is in the remove_duplicate_gids functions. It appears that the
qsort was sorting 'space junk' for the last entry.
If one looks at the logs, they are reporting one too many gids.
"remove_duplicate_gids: Enter 3 gids" even if there are only 2
My temporary fix in file system_smbd.c:
*grpcnt = ret; // was *grpcnt = ret + 1;
this is actually very similar to
Hope this helps.
Please retest against a current release and reopen if the issue is still present.