Voice memo sample rate is switching between 44100 and 8000khz.

Hello. I'm using an iPhone SE with the last iOS. I'm playing in a band and yesterday we rehearsed and I wanted to keep track of a couple new songs we wrote.

I recorded 8 memos and sent it to my computer to edit it. 4 of the 8 recordings have a good sound quality, I checked and the sample rate is 44100khz.

The problem is with the 4 others : it sounds like ****, I can't heard anything. I checked, and the sample rate is 8000khz ! What the actual **** ? Why did my phone switch to 8000khz ?

I thought "maybe it's becauce the memo is too long". Nope. One of the 44100khz memo is 15 minutes long, and one of the 8000khz is 10 long.

What's wrong ?