Haha found the issue I think, by mistake I left some old code in the skills file, so there were two Restore2 classes. Ren'Py coder said that might cause issues, so will update it. It shouldn't happen very often though, otherwise other people would have found the bug during the beta, since saving is a common activity!
update: game coder also said that probably happened only because you resumed an old game with an early version. Otherwise was impossible that nobody else found the bug during the 3 months of beta
So if you just start a new game with current version should work fine.