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.
Only sometimes. Other times it won’t post your comment at all. I still check to make sure my comments don’t post more than once but sometimes the lag is so bad it’s impossible to do even that.