Trying to upload a design pack zip file in Manage Packs – on clicking upload, after a few seconds, the screen clears with this message, “the link you followed has expired”.
Also, all the caches etc have been cleared.
When I look, there do appear to be a few react-dom.min.js errors (no idea if that’s relevant).
I came here because I was going to enter a new post regarding this exact same problem I’m having. It only happens on one of my sites. I also have an error, also only on one site (the same site) where I can’t save preferences – it says Preferences Save Error: Unknown error. WordPress may have logged you out. Try refreshing the page. I think these two issues may be related.