I also added the proxy network to both lemmy-ui and pictrs, but that did not resolve the issue.
I had to manually remove the sites icon from the database for the site to start working again.
I’m going to try removing the proxy network and instead use pictrs:8080 on the internal network as that feels more secure.
I checked this, and my lemmy.hconf file already has the host for pictrs set to http://pictrs:80.
The only thing that has worked so far is manually unsetting my site’s image icon by unsetting it directly int he Database.