Just an addendum - if you have a lock with a 4-digit user-changeable PIN code, then it is also quite normal that there is also a factory-programmed 8-digit code that the user can't change. Each lock with a different 8-digit code, and this code can be used to open the lock even if you have forgotten the 4-digit code.

The user gets a piece of paper specifying the initial 4-digit code (maybe 0000) and that 8-digit code that they should store at a different location as a backup. The factory could potentially keep a list of all serial numbers of produced units, together with the 8-digit master codes - but such a list is hard to make use of: how to verify that it is the legitimate owner of the lock that needs to be told the 8-digit number? And the list is very dangerous to have, in case someone gets access to it.

There should not be any single master PIN that can unlock all locks - such a code is too likely to get out in the wild when someone does something stupid. Like getting their computer pick up a virus.

So your lock that didn't like the removal of the EEPROM probably didn't like that the new EEPROM didn't have an 8-digit backup code and no valid EEPROM checksum/CRC/Adler/...