A family of Microsoft relational database management systems designed for ease of use.
We are experiencing this now on two different client systems, that had been working solidly for a number of years. (Azure backend data)
In both cases so far, the Primary key on the affected table has been an nvarchar(), these have both been legacy systems adapted to Azure BE data storage otherwise they would have a separate numeric PK field.
When we open the same database FE, with ostensibly the same versions of Access, we don't see the issue.
In both cases changing the field(s) type to varchar has fixed the issue, but this definitely appears to be a "silently distributed" Microsoft introduced bug.
This is the third or fourth bug we have seen in as many months with Access, I'm not impressed.
Edit - after some tests Access version 2204 does not suffer this.