Well, I"m not a yogurt expert, but I have made it quite a bit.
The instantpot - that's a pressure cooker, right? You aren't using the pressure cooking part of it, right?
Are you using an 'starter powder' or just the cultures?
This is the best site for trouble shooting and basic information - I've already gone to the yogurt section here with this link:
www.culturesforhealth.com/learn/category/yogurt/.
It may have been the temp was off, or even that the humidity was higher than usual. Once it's to at least the thickness of 'regular' yogurt, you can strain it through very fine cheesecloth to make it as thick as you wish.