Both Mastodon and Lemmy have this problem. Make the default where the most new content is, which is going to be the federated tab and all tabs respectively.

You should be able to use any reverse proxy to replace the one it includes, but you'll want to understand the various things that need to happen. Specific HTTP methods and content-types must be routed to the lemmy and not the lemmy-ui container, and not all of these (e.g. paths) are well documented...I just found this out the hard way: watch the caddy logs carefully as you are dealing with federation issues.

I sorted it out, and comments are now syncing. It was an HTTP routing problem. I had forwarded .well-known/, api/, etc, and /inbox/ (<--- note trailing slash) to lemmy's backend, but not /inbox. Once I did this the comments began to appear. Thanks all for the help, and hopefully this post helps someone else.

I should add that I get "Subscribe Pending" instead of Subscribed on any subscribed thread from any instance, if that matters or is a symptom of something.

Since I can't reply to anyone and am having to refresh other instances to see them: Languages were originally set to English and Unspecified for site and my user, I tried selecting them all and nothing changed. I can't see any of your replies locally, so I'll have to reply on the main thread :/

I guess it's obvious, but I can successfully post from my test instance to federated topics as well, so I'm not sure what isn't working.