Hmm on first go both jxh2154 (with 1.6 million tag edits) and my own profile (with about 60k) failboorued out, even after a few refreshes. That's the first my profile has failed that I've noticed in a long time.
Trying again a minute or so later led to both accounts showing up normally. Calculating tag edits is probably just a slow job and is preventing the profiles from being viewed right away. Once the page has been cached server-side and the job doesn't need to run, everything is happy again.
Not sure if it's a good idea for here and now, but maybe it might be a good idea in Danbooru 2 to do something AJAXy, and always load the profile, but display a throbber or some other "working..." indicator for the different slow running components until their data is available for display. That way people can get to their profiles, see what is available as soon as it is, and if necessary wait for the slower stuff to load. It'd be better than a generic failbooru anyway.