Exported .MP4 Files Unplayable on iPhone

I am hoping to find some answers as to why this is happening, maybe you've experienced this before. I've already searched every variation of this question that I can think of on Youtube.

So I am editing on my week old Windows laptop where I'm using my usual settings all around. My videos export quickly and successfully. I use H.264 ->  Match Source - Adaptive High Bitrate. The videos play fine in all of my laptop's built-in players, but when I send the clips to my iPhone using ANY method (airdropping from a mac, snapdrop, google drive, dropbox, sd card) the videos are rejected by my phone. Photos app says it can't receive them. Files app downloads them, but when I click play it's blank. SnapDrop receives them but never gives me a download option. They play while in dropbox and google drive. They also play on my mac. I've restarted my phone and it's up to date. Premiere is up to date. I've done tests with other video files to rule out the possibility that there's anything wrong with my phone.vI think there must be something wrong with my export settings or the way that PCs export?

I'm trying to remember whether I have exported any videos on this computer that worked on my phone. I think I did, from a different project.

Thanks in advance if you can think of anything!