Ok, thank you for your help.
But this problem only occurs when I delete Autoptimize… so surely it has to be causing it?
This is what it should look like (currently still has the Autoptimize plugin): https://www.smalldoorvet.com/
sdveterinary.wpengine.com
It’s a staging site so there’s a login – here are the details: https://onetimesecret.com/secret/r3mqrtb8tpszh8nhqz7jl2y1fb4tneq
Neither of these suggestions worked. Deleted all caches and deleted everything related to Autoptimize in the wp-content folder -> no change. Any other ideas? Please help!