This has happened at least four times and it's a pain. I am using a page with UDL as an explorable "world map". After navigating away from that page and coming back to it at random intervals, all the explored areas will become unexplored. Additionally, I use a token that can be used by all my players so they can have a vision of where it passed through. I noticed that after the token is dragged for a few seconds continually it randomly stops revealing areas and all of my players lose access to its sight. To fix this I have to drag the players (and me) to another page and back to the "world map". Seems the distance travelled and the suspension of the area-reveal seem to be consistent. What this means is that if I want to use the token to reveal areas, I will randomly lose sight of all the explored areas and to re-reveal those areas I will need to change pages a couple of times (which can and did trigger loss of explored areas).