I do use Calibre, but I don't have any good alternative, so if that's the cause, I'll just have to keep resetting my Kindle.

I have the same problem and just press on\\off.  
Do you use Calibre?   
I do and I heard that formatting books through this program leads to errors in work of Kindle devises.

I have a Kindle Oasis, the 2019 model. Often, when I long press a word to read the dictionary definition, I get a page flip instead. A reboot fixes that problem for a while, but then it reappears. Rebooting takes a minute or two, so I'd rather not have to do that. Is this a known problem? Do any firmware or other updates fix it?

Kindle Oasis 3 keeps switching pages when long pressing a word