Same thing happens to me in long enough sessions in xterm. Anecdotally it's pretty much guaranteed if I continue a session close to the point of context compacting, or if the context suddenly expands with some tool call.

Edit: for a while I thought this was by design since it was a very visceral / graphical way to feel that you're hitting the edge of context and should probably end the session.

If I get to the flicker point I generally start a new session. The flicker point always happens though from what I have observed.