Strange, I disable it during combat because otherwise leads to bugs, but after a fight it should work again. Maybe try to do a combat and see if works? Otherwise need to ask Ren'Py coder since I'm not sure why that happens!
As it happens, it fixed itself just now. A combat was not the cause, but rather, the main story advancing. I've just hit the deadline and somewhere after passing out the rollback is working once more.
