Mac Photos App changed imported Videos from PM to AM

Hmm. Often, the first things we try to narrow the possibilities are these:

• Restart the computer (of course)
• Re-start in Safe Mode. This bypasses certain potentially disruptive processes. Safe Mode is different for different computers, so see this: 

      Start up your Mac in safe mode - Apple Support 

• Use another library if you have one, or make a small test Library with a few pictures in it and see if the same thing happens. You can create a new Library by closing Photos and then option-clicking on the Photos icon.
• Make a new user and see if the same problem recurs with it

The idea is to find out if the problem is with the Library, with your account, or with caches and login items, and stuff like that. One of these steps may fix the problem, but their failure to work also helps figure out what's happening.

Let us know if you find anything....

Seems pretty odd. How are these videos "imported?" Do you use iCloud? Do you use File>Import? or what?

Does this happen to still pictures? Can you see a pattern with the videos, like order of import, which you may be able to see in the Imports folder, depending on your method. Or maybe file size, or frame rate?

What phone? OS? Any changes from AM to PM? What time zone do the pictures indicate?