Sometimes the chat bubbles lock to the top left of the screen when created, or when the speaker moves out of the FOV, and in extreme cases, scale to fill the whole screen (sometimes in a way uncontrollable by the player, blocking out the view for a few seconds).
Reproduced in Jailbreak and a place by bizbot19. All you need to do is play a game with other players who are speaking with chat bubbles enables, and play around with movement and the camera.
Just started happening. Could this be related to the BillboardGui fix?