Premature License Expiration

Possible reasons involve

• wrong clock setting (check this first)
• detected manipulation of the clock (going backward multiple times)
• usage of the same license file on several machines
• sophos can deactivate a license if inappropriate use (not as home system) is reported
• unlike XG there is no requirement to be online at least once in 30 days

In case clock correction does not help re-image the system, re-apply the license and install the last configuration backup.

Wrong date settings when registering, we don't have the 3rd november 2023 yet.

Incorrect. That date is March 11th, 2023.

Ok, my bad, we write the date different than you.

From the licensing portal, I deleted my existing license, created a new one, uploaded and applied the new license, rebooted the UTM, and am now able to login again.

It's back again. Appears to reoccur after a reboot:

As said earlier: check the clock.

ssh into it (should still be possible) and try "hwclock".

Maybe the battery for the clock (usually a CR2032 button cell) died, the box comes up with a faulty date (earlier than 03/11/2023) and later learns the correct time via NTP.
"dmesg" or "cat /var/log/messages" should show the entire boot process with timestamps.