We're aware of the problem but not sure what causes it. I think it may have to do with the API that got bonked when we updated mediawiki. Unfortunately the plugin is very barebones in its documentation (it's not even supposed to let you try and create a book currently and has been in that state since 2019 lol, you have to manually disable this in the files). As you can see even the error message is barely an error message, it just says "there was an error" but doesn't specify which one.

It sucks cause we had barely turned it on when we learned we had to update mediawiki and the update bonked it, but because of the lack of documentation and since it relies on an external service we don't control to actually render the book it makes bug-finding difficult. If our API is the problem as I suspect then I have no idea how to fix that lol