Resource Assignment budget units spread moving with no known reason

We have been using the Resource Assignment window to manually enter month to month budget (manual curve) to project forecast.

The budgeted units are generally mid activity (i.e. not at the beginning or end of the project). This has been standard practice for about 4 years.

Recently, without explanation, the units shifted to bleed over into the next month.

This happened to multiple projects with different project managers. There doesn't seem to be a common thread (i.e. they weren't all scheduled).

Has anyone else witnessed this before?

One thought was that it was how the spread was displayed (month vs. day) and the definition of month rolled to the next week. However, everyone is using display by day.