How can I keep iCloud Photo Library from harming the frame rate of my videos?

I uploaded my library to iCloud a month prior.

When I try to record videos in crisp 4K 60FPS, the video quality and frame rate will be perfect (as recorded) for the first 1-2 weeks when I rewatch it in the Photos App.

However, when I reload those same 60FPS videos on my Photos App once more after that time period, some of these videos have reverted to 30-45FPS even when "fully downloaded" or loaded.

This is seriously irking me since I paid a significant amount to get a phone capable of not only recording, BUT KEEPING 2160p60 videos, and if anyone can tell me how to keep this iCloud Photo Library from damaging my frame rate, please answer.

Thank you.