Hey,
for us the reason was a missing setup:
The worker was absent, but there was no Absence Code set.
Please check:
Time and attendance > Setup > Groups > Absence groups
Human resources > Absence > Absence codes
Now it should be possible when the worker clocks in
to set an absent reason.
If not maybe you should think about creating a new worker,
which also settled some of my problems, but it was a sandbox only.
For a live production system I recommend to ask an expert Consult for help.
The best Blog out there for this topic:
https://dyntips.com/ax7ta/