Unable to connect iPad to Epson projector

In giving a presentation recently and planning to connect my iPad to a fairly new Epson projector, I discovered on lining everything up that I couldn't get a connection. The projector saw no input source, the iPad nothing new in Screen Sharing. I was using a known good Digital AV adapter and good HDMI cable (in fact unplugged the cable from the MacBook it was using to successfully connect to the projector). Only limited time was available for troubleshooting there, nothing beyond trying connections, making sure all secure, unplugging while running a quick reboot on the iPad, to no effect. This was something that I managed to do successfully on many occasions in the past, admittedly not within the last couple of years at least.

I did catch a quick glance of a popup on the iPad screen about "... downloading accessory updates..." or words to that effect, which reported failed. Not surprising, as no cell coverage inside that hangar and I wasn't connected to the local wifi.

Once I got back home I pulled my own LCD projector out and hooked everything else up again, using a known good cables and the same adapter/dongle, and got the same failure to connect. Extensive troubleshooting, trying every combination of all discovered suggested solutions, yielded no change. While still unable to connect to the projector, the iPad/dongle/cable arrangement had no trouble at all in hooking up to the TV.

I had wondered if trying on a different projector would result in another of the abbreviated popups, that the download of whatever was missing would take place, but that did not happen. No similar popups were seen on multiple tries, again in combinations of cables/adapters/sequences of connecting/restarts on both iPad and projector/etc.

Subsequently two or our IT guys took their own iPads in to check my gripe out. Both are about the same as mine, either 8 or 9G and with current iPadOS. The first to connect had no problems at all, but when the second plugged his in he got the same no connection problem. He also got what sounds like the same popup message displayed, but in his case he was connected to the local wifi, his download completed and after that he was able to connect again.

I'm at my wits end, totally out of new ideas to try. It seems likely that if I could induce the download of whatever it was they wanted to shoot down to me that first time, that has a chance of fixing this; does anyone have a way I can force that to happen. Or barring, that, any other things I might try?

Sorry for the length, thanks in advance for any steers or assists you can help me with.

[Re-Titled by Moderator]