Ok, just throwing things out there that I would have come across in personal experience and would check.
Sometimes database queries get cached on DB side, it takes long time to load original request, but any future requests for same query come up super quick.
Like you say, it does not make much sense that changing method name alone makes difference.
Maybe check if you have any queries running on DB, pretty sure I had similar case only recently where first DB query would not fail straight out, but just case 500 error, and refresh on same page loaded everything. It was SQL related issue in the end.
