UPDATE: Microsoft is working on a solution for this problem and since originally reported, it is now known that it affects 1803, 1709, and 1703. There is a workaround, however. See: Customers Still Using Access 97 Databases Affected by Windows 10 Patch Tuesday Updates
Microsoft is off to a sound start for 2019. As the days have progressed past the company’s first Patch Tuesday of the year, bug reports are continuing to roll in.
One additional bug has been uncovered by some customers in that after installing KB4480966 for Windows 10 1803, .mdb databases are unrecognizable.
So far, no workaround is available and Microsoft hasn’t yet acknowledged if its a widespread problem or not.