When opening one of these errors, no further information is given.
Yeah, unfortunately these errors are not always the most helpful. What does the response from the server say if you use your browser dev tools to inspect network activity? Do you see any errors in the browser console? And what version of the stack are you running?
Also worth noting that there is a max buckets setting that gets applied in Elasticsearch, as described in this thread:
It doesn't sound like you're running into this based on your description, but thought I'd mention it just in case.