About half my replies simply disappear once I hit Comment: Firefox

As per the title, when I hit reply on a post or comment, once I make my reply and hit Comment, about half the time the comment simply disappears forever. This happens across all subs, and several different handles, and includes subs I mod (ie., I can confirm these posts aren't getting automodded or removed by reddit). It just happens constantly. I've taken to copying my replies before hitting Comment, since I know there's a high chance the comment will disappear

Seems to happen most on firefox using www.reddit.com (have never seen this happen on old reddit or the previous new reddit). I sometimes post using Relay for Reddit from my phone, never happens on that.