Per Stained Glass:
Whatever is causing it, it is not the individual devices. Individual devices can be prone to not playing well with Buzztime, but not all at the same time. We have never had the sort of problem you had at Bull's Eye, and the only rare times we had significant problems, it was WiFi problems.
Poor wifi can cause problems with multiple devices and the Sitehub itself, and bars often have poor wifi, so that is worth checking. You would like to get readings on signal strength (you'll get a measurement like -60dbm) and throughput (you'll get a measurement like 40mbps) . Unfortunately for you, Nanny Apple does not allow third-party apps to precisely measure signal, so you would be better off using an Android device for this. Using WiFi Analyzer and Speedtest will do the job, especially around the time these dropoffs occur. If things go bad then, then that is a big clue. Another test is simply to use the wifi in a different way before and during one of these events. Are there any problems there?
The regularity of the disconnects seems to point away from poor wifi, though. Buzztime does run periodic location checks on a device, and it will disconnect a device if it is not happy with what it finds.
You know Buzztime is doing a location check if you see this symbol on the top left or right of your screen:
Attachment:
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It's important to understand that the Sitehub does
not transmit the game to your devices (it does to your TVs); if it did, you could not play up to 2 miles away. Your devices communicate with a Buzztime server in California. What the SiteHub does do is provide information to that Buzztime server (whether or not the game is on, maybe the location of the place). I know from my own experience that Buzztime will usually do a check shortly before a new game begins.
You will say "But this isn't happening at that time!" True, but electronic devices can have malfunctioning clocks, which will mess up location checks. I have a tablet that thinks it is October 2025, and it must have its time adjusted each time it is turned on for the wifi to work. Here, it would be a matter of the SiteHub not providing proper time, which might be an internal problem, might be a matter of someone not setting the right time in setup. This is why a new SiteHub would be a good idea, if only to eliminate it as the cause.
Besides that, all you have left is some unknown factor unique to your location that is causing your problem, and at this point I'm really grasping at straws. You've had two modems and a SiteHub develop problems in short order; there could be a common reason for that. Could you describe the modem problem with a bit more detail? How was it alike/different from what you are getting from the SiteHub?
Diagnosing these problems is sometimes like diagnosing a patient; sometimes it isn't simple. If you go to the doctor with terrible headaches, it's likely migraines; it might be a brain tumor; it could be something else. So you go through a series of tests to separate the actual cause from the possibilities. It's the same here, except it's easier to swap out parts to see what is bad.

Here, the situation is not clear, and the clues you do have point in different directions.