another issue is if you take TOO LONG in making your post & get signed out automatically for inactivity.
lots of sites sign you out... even though you can still type in "the box".
hotspot/jetpack connections are also famous for causing this to happen for the same reason.
heres how you fix that:
IF you think thats happening.. after you finish typing & BEFORE you hit the submit button...
do a ctrl/c (copy) of everything you just put in the box.
then if it did sign you out? all you gotta do is go back to the box & hit ctrl/v (paste)
happens all the time to lots of us.