My guess is that it’s something in the theme, but that’s only a guess, some type of filter that is altering post excerpts. If it were me and I had just started building the site I would just delete the groups and import them if I have json files, however, that will not solve your problem since it might happen again if you don’t figure it out.
I would keep trying to do whatever you did that made them disappear with different themes/plugins enabled to figure out what caused it. other than that, I don’t think I’ll be of much help. If you can tell me exactly the steps and what combination causes it I might be able to help more, but you’re going to have to narrow it down.
