If it prevents you from playing, try reaching the pingpong scene again, something in the save got corrupt
Yes, this is a known annoying bug I need to fix )=
For some reason that specific save get corrupt in some rare scenarios,
you can:
1. load a prior save and go again from there (the easy solution)
or
2. Get another save and edit it, take what it has under the checkpoint fields and paste it to your corrupt save.