Hello,
For sure an RMSE of 30+% would not be fun to see.
A few things:
There’s not really any reason to think that upgrading from v11 to v12 would cause an appreciable change in RMSE for FSRS, as they are nearly identically the same deck/s.
I don’t know anything about your review history or collection but one thing that stands out to me is that, at the top of your screen, the current preset is only used for a single deck:
Is it the case that your entire collection is only one deck?
There are a few potential confounders here, related to your deck presets, optimization, collection organization, a handful of other things. But, ultimately, I’m sorry to say that the question is, in all likelihood, an FSRS question rather than an Ankihub question. While I’m reasonably familiar with FSRS, troubleshooting it is probably beyond the scope of what we’re able to help with, aside from the basics.
If you really want to get to the root of the issue I’d recommend reaching out on the official Anki forums where some of the FSRS devs and authors frequently hang out and you’re likely to get more expert FSRS-related advice there: https://forums.ankiweb.net/
It also appears that one of the authors of FSRS has responded to your post on Reddit, which I would give good shrift:
Please let me know if that answers your question, and if there’s anything else I can help with. 