It may be unrelated but I recall coming across a post in the past that mentioned that MusicBee's date format follows your system settings.
So if your system settings aren't using that date format, you may want to experiment with changing it to that.
As a last resort, I personally would use the "search and replace" tool to change them back to the desired format.
100% sure that i, anyone or nothing else, didn't change that on my system.
Anyway, i found a workaround by creating a vitrual tag using the formula below to copy the values in the previous format.
$Date(<Date Created>,yyyy-MM-dd)