Premiere Elements 2021 frozen halfway through project
I'm doing my first project using mainly footage shoot from my iphone 11 pro, plus stills and a few HD clips from old family videos mixed in. The project settings were set by the first clip added to the timeline (an iphone clip).
I was going along fairly smoothly with the occasional freeze up, until there was about 8 minutes of media in the timeline. Up to that point, a message popped up a couple of times indicating that I did not have the proper codecs to support HEVC/HEIC, but after following the instructions, it appeared that the codecs were already installed, so I powered on.
Now, with 8 minutes of footage:
- only a handful of the dozens of clips in the timeline and asset panel have a visual thumbnail
- the project won't play, and when I try to scrub, the only clip that plays is the HD clip
- the project won't close normally, and I have to use the task manager to close the project
I've also tried:
- uninstalling and reinstalling the program
- increasing my RAM from 16 to 32 GB
- contacting the Adobe chat (but they don't recognize my product as registered even though it is, so I can't start a session)
- updating my drivers from the computer, videocard, etc.
My Adobe program and project files are on my (D:) hard drive, as my SD boot drive only has 17GB of space left. The cache files end up on my SSD boot drive, and I delete them when prompted. All of the other scratch files are set to store on the 1 TB hard drive with 700GB still available.
I've included below my system info, video card info and media info for both the iPhone and HD clips, as well as a screen shot of the General project settings.
Is it a codec issue, hardware issue, project management issue (i.e.user error)?
Any help is greatly appreciated.

Video card

iPhone clip

HD clip

General project settings

