This happens on older versions of ruby and rails.

Solved by downgrading psych:

# Gemfile
gem 'psych', '< 4'

The solution is, make sure that the file /etc/fuse.conf has the following line:

user_allow_other

Seeing this ^ error and currently don't know how to fix it. It happens only on some of my (presumably identically configured) websites. This is happening when a user attempts to post any comment.

Turns out, this was due to a workflow rule that attempted to email the author of a parent-comment and notify them that their comment has been replied to. Since there is no parent comment, there is no email to send a message to, which was causing the error.

If you're having problems with a local copy of stable diffusion experiencing a connection timeout.

I've solved it by allowing websockets in my nginx proxy, like so: 

I spent way too much time on this not to share the solution. : ) You can find the tl;dr at the bottom.

The problem appeared to be a lag, but since none of my components are top of the line, I wasn't sure where exactly the problem was. Was it the Intuos tablet, or something else? I suspected the software, Krita, and spent some time tinkering with it, configuring caching, and adjusting rendering configuration. That didn't help.