As a lemmy user in an instance, is it possible to tell the instance to fetch missing post/comment ?
So, I see some comment, post view from my instance is missing comparing to view from that original instance. Which prevent me to interact (like, comment)
As a user, how to tell the instance to update missing content ?
There's been a bug in lemmy that makes posts really slow. Check the version your instance is running, i believe most of the bug was worked out in BE: 0.19.3. That info is at the bottom of the page
If you're instance is running that or newer, the admin might need to reboot some of the services or the server.
If you're not on lemmy world, but the poster/community that you're looking at is on lemmy.world, that could be your answer. Due to the way lemmy currently processes federated content, lemmy.world is big enough that many other instances aren't able to process lemmy.world messages as fast as it produces them, meaning that the smaller instances fall ever further behind lemmy.world
If it's due to defederation, no. If it's due to defederation, your only option is to choose a new home instance.
One thing you might have done is have deselected the language (including "unspecified") on your home instance. That would hide comments and posts tagged with that language. I did that inadvertently. If that's it, just turn it back on.
Or you could have blocked the user or instance on your home instance, and if so, you can unblock them.