We get this a bit on my instance as well. Much less if you run two load balanced ui instances. The latest lemmy version says it fixes issues with certain blocking actions on rhe server, which I have high hopes for it fixing issues like this.

Looks like programming.dev is now a couple of versions out of date, bringing it up to date might help.

The admin team are aware of it, and last time I asked it was due to some database queries for stats updating. The latest Lemmy version does claim to fix something similar, but I haven't confirmed with the team that its the fix.

I'll ask on discord if there is a plan to upgrade.

The admin team are aware, and are planning on upgrading to the latest lemmy version in the coming days.

504 errors sees like a lot.