Transient Connection Error on NEC Displays in Room Controls

[neve]

has anyone else seen this?
In two different zoom rooms with NEC displays, the displays have started failing to turn on and off for meetings. When I go into manual Room Controls at the iPad or virtually in a browser, it looks like this:

 

If I click on Retry, the devices all work fine for a minute, and I can turn the displays on and off. Within a few minutes, the connection errors return. Retry always fixes the problem for a few minutes. The NEC projectors are not affected.
In both rooms, the displays, projector, and Zoom PC are on their own dedicated room AV switch. No display firmware has been changed. This room has been working well for 3 years, and the room profile has been unchanged for almost two years.
I've opened a ticket, but as usual, it's hard to get past the "have you tried power cycling" stage.