With the sluggishness of the site these last few days you can sometimes get slowness or infinitely loading icon when hitting submit. If you aren’t sure if your post submitted, refresh the original page in a different tab before hitting submit again to see if it went through. I see double and triple posts in almost every comment section.
Yep, it’s called an idempotent key. The server gets a request with a specific key (usually a random guid), stores it and ignores any further requests with the same key. It would be a great addition to Lemmy.