I have noticed posts going missing every once in a while and not sure if I'm doing something wrong or if it's a known issue.
For example I wrote a short welcome post for https://lemmy.world/c/dnd but I can no longer see my own post on my own account. But if i log out and navigate to https://lemmy.world/c/dnd I can see the post is there and fine?
Check your language setting has all the languages you want selected and ALSO has undefined selected too. V important and it's been causing a lot of issues, definitely needs looking at by devs.
I'm using Liftoff also and it doesn't look like this setting is in there yet. You can do it from the mobile site though.
If you're not sure how to get to that, go through Liftoff by visiting settings > accounts > tap the account name > three dots in top corner > open in browser.
Ah, that's a shame. Tbf it might not be anything to do with you it might just be part of the ongoing federation issues we've been seeing as everything struggles to scale up.
You can always force your instance to index a post by searching the URL, if it's something you really want to reply to. And searching for a comment URL will pull in that comment, any parent comments, plus the post itself.