Bug in latest Office update affects Access’s ability to recognize Identity Columns in linked SQL Server tables. This bug affects C2R installations of Office 2016, 2019, and O365.
If your application refreshes existing links or creates new links to the SQL Server tables, these columns will be recognized as PK (if they are), but will not be recognized by Access as an Autonumber. So, when you do an insert, the record will be created but no Identity value will be assigned and it will generate an error message during when you attempt to save the record. More info from Microsoft: