Screen Recording on Quicktime - Audio first works for 10 mins, then static, then silent

My MacBook Pro is a 13-in 2020 with an M1 chip. I'm also on Big Sur Ver 11.4.

Hello,

I've been evaluating some performances of my students. I use Chrome to watch them but because it's live, we record them too if we need to go back and check something. I use earphones.

I record the screen + audio by going into System Preferences -> output -> click 'screen record (audio), then input -> Quicktime Input. Then I go to Quicktime and screen record.

For EVERY week I've done this for, the recording is great and everything works perfectly for the first 8-10 minutes. But then the audio starts to become extremely static-y (like something out of a horror movie), and after a few minutes of progressive static and voices sounding deeper/lower, the audio turns silent and only picks up/records the noises I make from my earphone mic.

I know my earphones are not the problem because I have an older, 2015 Mac on Sierra which still works perfectly.

I'm pretty furious right now because I can't seem to fix the problem and this has happened for months, putting us in a difficult situation. I can't use my 2015 Mac either because these recordings take up a ton of space and I have no more memory left.