Does the hidden file say,
.hidden: core file (Xenix)
?
If so, it indicates that a core dump occurred and places that marker in the directory location where the dump occurred.
You can check the status with
cat /proc/sys/kernel/core_pattern
If it was an installation fault, for example, you may get a path like
Also, you may check /var/lib/systemd/coredump to see if anything there.
If empty, I would not worry too much about it and just delete the harmless ~/.hidden file and keep your eyes peeled to see if it is generated again, later.