I'm getting this too, but I've not tested it enough across different instances/communities.
I'm trying to respond to something on a different instance. I did respond to one comment, and then the next I went to throws this error (so I tried on 2 other browsers and Connect with no lick). Dunno if it's a rate limit or something, as I've cleared caches, cookies, logged in/out, triple checked language settings, etc.
Edit: yay at least this comment worked!