That's all I know. This was from the logs... I'll enable socket.io logging and see if that shows everything. It's not doing it anymore but I'll keep a look out for it.
Search 500 errors here.
In a strange twist of fate, I tried searching to see if someone had reported that the search wasn't working, but the search wasn't working. Reloads the page you were on rather than going to the results. Trying to load the search directly offers a 500 error.
Should be fixed now. Updated the solr plugin to latest.