I have, on many occasions, had error messages appear in the log file and been completely unable to locate the source.
They very often contain no information on which plugin, sensor, frontend card or whatever is causing them. And it also not easy to get help from this forum on this kind of problems.
My last frustration is here:
With you on that.
Twice I’ve had a bizarre start up error where nothing in configurations.yaml has changed, but HA launches into “Safe Mode” and complains about all my HACS plugins.
Well, after moving all plugins out of their directory, commenting them all out, removing all references to the sensor/services using the plugins HA finally boots!
Then undoing the damage doesn’t cause an issue on HA.
Big ol’ game of “pin the tail”…
What level of logging do you have setup. maybe easier to see if set the logging level to debug to get further info
maybe of help. Invalid HTTP Method
https://www.reddit.com/r/homeassistant/comments/8g4xrt/invalid_http_method_log_every_2_seconds/