I often get that or similar gllitches on FB, e.g. nothing appearing when I type. (It's as the website design's not the best, but maybe it's just heavy traffic, or patches of slow connection along the way, or an auto update in the background).
I find that leaving plenty of time between each action and the next one usually helps.
Another thing that often helps for me (with a phone, at least) is to end the Facebook session by going to some other website, and enter it again with a fresh start, e.g. via browser history using the oldest, simple-looking link in the ended session. That may be because I sometimes unknowingly touch a link and, because I've zoomed in, don't see the popup that's waiting for input re leaving the page (I use desktop views where possible). Or because some video's appeared and hogged the bandwidth.
If that doesn't work, emptying the cache for all apps often helps (Facebook leaves quite a lot of clutter around).
Even when typing has no effect, pasting usually works for me once a cursor's appeared, so I can use a document. I compose in Google Docs (leaving the browser exactly as is, so that the place in Facebook hasn't been lost forever).
(Of course, after trying all that, sometimes it's just a local internet slowdown that I hadn't noticed!).