My phone keeps going to "slow charging".

My phone (Samsung Galaxy S20 FE) is currently on 15%.

When I first plug it in, it says "1 hour 54 minutes until full", which is what I expect.

Then after a minute or so, regardless of whether I touch it or not, it changes to 3 hours 39 minutes.

That used to be where it ended, but today it's started saying 5 hours, or even 11 hours.

This happens with every charger I own, and again it changes even if I don't touch it. Is there anything I can do?