A good starting point would be to disable all third-party plugins and see if that resolves the issue.
Imgur Plugin error invalid-refresh-token
Hey guys, I'm having problems with the imgur plugin, did everything as the steps say but when trying to upload something I get invalid-refresh-token.
I'm not the only one it seems https://github.com/barisusakli/nodebb-plugin-imgur/issues/21
Thanks in advance