Well, for me rails is… well, more than just difficult.
But 500 is error of the server. There is big chance it comes from some plugin, but it can be mis-configuration too. Safe mode can give a hint what is broken, if the issue happends on user’s side. But if something that changes functionality is broken in serverside then safe mode is toothless.
Sure, you can disable every plugins and rebuild to see if the situation will be fixed. And after that start figuring out which one. Or at least disabling all plugins that aren’t by Discourse — and even that isn’t totally sure because every official ones aren’t here in use.
But that takes quite much time. Perhaps it’s wiser move to wait until someone who actual knows chimes in.