For some reason I suspected it had to do with 'Imgur Client ID', so I went ahead and clear it, leaving it all empty, then I tried to change my avatar and upload a new one. It resulted in this output:
[root@fretzchnid]# info: Attempting upload to: /root/nodebb/public/uploads/2-profileimg.jpg
throw er; // Unhandled 'error' event
Error: spawn ENOENT
at errnoException (child_process.js:980:11)
at Process.ChildProcess._handle.onexit (child_process.js:771:34)
+ Exit 8 node app (wd: ~/nodebb)
(wd now: ~/nodebb/public)
The folder 'uploads' is owned by root and is chmoded 777. I run this NodeBB as root.
I should also note that it only crashes the instance (the issue) - the avatar is actually uploaded and applied.