Text format keeps resetting with page turning

Hi, I have an Oasis 9th gen. This has happened before and it just fixed itself, I don't really know how.

I was reading, I turned a page, and the format of the text suddenly changed. Font size, space between lines and line layout, everything except the font type. I change it back to my settings, turn a page, resets again.

It's super annoying and it's driving me crazy. Why does this happen out of the blue and how can I fix it?
Thank you in advance!