Can't open any FLV with MP4 files in it

Hi.

I'm an animator who works on Animate CC, and a few months back an odd error showed up: I couldn't open the files provided by my studio anymore without Animate just instantly freezing. It will not respond, no matter how long I wait.

After some trial and error, I figured out that this error only occurs when there are MP4 files in the library. The same issue happens if I try to import an MP4 file into a pre-existing file. Unfortunately, my studio uses MP4 files for storyboards, so that makes any work impossible to do. My workaround so far has been using a separate computer to delete said MP4s from the FLAs, convert them to FLVs and put them back in. That option is no longer possible for a few reasons.

Over the course of a few months I have tried absolutely everything I could think of: 

• Fresh reinstallation
• Tried installing multiple versions of Animate CC
• Reset preferences
• Updated drivers
• Updated Windows several times
• Several other things that I can't remember at this point (I'm aware this isn't exactly useful, I apologize)

The problem definitely comes from my computer, since my small laptop can open those files without issues. But I'm out of ideas as to how to fix it.

I'm on Windows 10, latest version. The latest version of Animate I tried to work with is 22.0.3.