64 bit Operating System, x64 based processor (Windows 10 with latest updates installed)

Type KB5001330 into the forum search and see if that has something to do with your problem.

These are the updates installed on my PC, I don't see the KB5001330 update here.

I also have the .mts problem (MS16Plat). Sadly, KB5001330 seems to apply only to Vegas Pro.
I've been using MS since 2006, initially with Pana GS camcorders, more recently with a TM700, which is the source of the problem. My ad hoc solution to date has been to convert to .mp4 with Handbrake, but it's a bit of a chore when there's more than a handful of clips to deal with. On the latest crash, with a big .mts project to do, I actually completed the offered report form. Magix immediately sent a new install file, title ending _Update4.exe, for which my thanks, but there's noticable difference from my original install. So I spent a morning trawling Google, but every solution I found involved external file conversion, thus my presence here (first time in several years) looking for help.
Seems I was right with Handbrake. You can't win them all!

I've sent a support request yesterday so hopefully this can be resolved.

Let's hope you have better luck.

Now here's a strange thing:
I had been watching the activity in a nest of young birds and had taken a sequence of clips. These were each around a minute long, with a minute or so between them. Without thinking, I dropped three .mts clips on to the timeline of a fresh MS16 run, only realising what I'd done when a fourth clip was rejected. Then a fifth was accepted! I could find no technical differences between clips in the whole batch of eight or so, but about half would always be accepted and half rejected.
I wonder if paul-s will get any sort of answer.