Keep in mind, defederation is bidirectional. You can end up on an instance that doesn't defederate anybody but is being defederated by some major instances and end up worse off. Also, communities are bound to an instance so even if your instance doesn't defederate with another, the instance that hosts the community might, which also doesn't solve anything.

Also lemmy.ml had to restore from backup monday because postgres shat itself, so if the post is from monday or around, it's possible it was simply lost due to the technical problems.

There's also some federation problems with 0.19.0 and 0.19.1, so it's possible it's been attempted to be delivered to lemmy.ml but failed due to load or whatever.

You didn't give any details or examples so we can only speculate. We troubleshoot federation by establishing patterns, like from what instance are the missing comments from, what instance hosts the community.

Addendum: I've also been experiencing occasional ghost posts, and I'm on my own instance, so there might be some stuff going on that's unrelated, because I sure didn't do anything. If they were deleted or retracted I would see them because I'm admin, I see everything.

Last Lemmy version had federation issues - the current one (0.19.2) supposedly fixed them. New threads should be populating correctly now, maybe give it a couple of days and check again?

If you do want to switch, the instance I'm on only blocks pornlemmy.com, ds9.lemmy.ml, voyager.lemmy.ml and enterprise.lemmy.ml: https://reddthat.com/instances

None. An instance that federates with everyone will end up defederated themselves, because they'll end up full of bigots and trolls

Make sure you go to Settings and select any languages you want to see as well as Undetermined - I had a similar issue which was fixed by doing this.

If that's not it, it may be a delay in comments federating if it's a community you just recently subscribed to, or there could be federation issues. If the post is on an instance that's defederated with yours, I don't think it would show up at all, unless the defederation happened after it was made.

You can check who an instance has defederated with by checking the Instances link at the bottom of the mane page (or adding /instances after the URL). There's also a tool to see what other instances have defederated with a particular one here: https://defed.xyz/

I think lemm.ee is least defederated instance

It's not defederation - hardly any instances block lemmy.ml, not even beehaw.

The more lenient ones I've tried are midwest.social and lemm.ee

I had this issue. Go to your lemmy login settings. If your language is set to undetermined, try adding english. That fixed it for me.

Currently, the big problem with federation is that some instances are running newer software than others. Causes lag and other weird problems.

I don't think there's any single instance that hasn't either defederated from someone or been defederated.

lemmy.sdf.org

I think Lemmy.today doesn't defederate.

What’s the post in question?