Stuttering 24/30FPS Playback in Android App

So I'll start by saying I have an underpowered phone. I'm using a Motorola Z3 Play. That said, most of the functions in the app work, and work acceptably (except maybe the tracking feature). Tonight I did some experimenting with the 4K mod on my One R. I recorded 3 30 second clips:

1) 4K, 16:9, 60fps (ended up at 76mbps bitrate)

2) 4K, 16:9, 24FPS (ended up at 78mbps bitrate)

3) 4K, 4:3, 30FPS (ended up with 66mbps bitrate)

File sizes were similar at around 250-300MB each. In the Insta360 app, the 60fps clip plays back BUTTERY smooth. No issues htere. However, both the 24FPS and 30FPS clips BARELY play. They stutter like crazy and play maybe one or 2 frames every second, if I'm lucky. I'm having a hard time believing it's bitrate since they were all so close (but also well under the advertized 100mpbs for some reason). I was also recording in H265. I know that's a demanding codec, but if that's the case, I can't explain why the 60FPS clip plays smoothly.

For the record, in Studio 2020 on my Windows 10 machine, the 60FPS and 30FPS clips play fine, but the 24FPS clip is a LITTLE jittery.

Has anyone else experienced this or have any ideas as to what might be going on?

Thanks for any help.