So yeah as the title states I have seen this since the back end of last year.
Latest version is Engine DJ v3.0.0
Open Engine DJ & it loads tracks ok which have mp3 tags with date created & modified etc.
Pop some into Collection - all good
Go to Collection pop some onto USB stick - all good
Go back to ‘Files’ & all the track’s ‘Date created’ reset to 01/01/1970 !
It looks like the tags aren’t being read when load tracks.
Only way to get the correct dates back is to close Engine & restart.
If you Google that date you can see it’s commonly used ‘default date’ in databases. The nerd side of it is way beyond my understanding but it makes pretty interesting reading how it came about.
It may also go some way to explaining away the issue you’re having.