Hi Sada,
There should be two possible reasons:
1, you are using HR replication for this user/organization, so it will be overwritten by HR settings.
2, maybe someone removed this with trx ppoma_bbp.
For the second reason, I suggest you activate the log for change values in ppoma_bbp according to the following KBA:
1617444 - How to activate the log for values changed in PPOMA_BBP to SRM 5.0
Then you can monitor if someone deleted this attribute by accident.
Best regards,
Ivy