I feel like this might be a copy/paste function issue. After recording that video I managed to update the rest of that page by typing in the class name, and clicking it from the suggestions list. The problem didn’t occur again. I’ll keep using this process and if it continues to work, I’ll post another reply here.
Thanks so much for your report and getting back with updates!
I was able to reproduce the issue and I’m pretty sure I’ve found the main reason
We updated the builder save to only save data that has been changed and it seems, one or the other check for adding or removing classes is missing (sometimes classes remain in the frontend even though they were removed in the builder).