Just closing the loop on this since I have had sufficient time to arrive at what I believe to be the locus of the issue, and things are working reliably.
I realize a lot of people assume the inexpensive 12v 5A power supply provided by the mount manufacturer will drive everything plugged into it. That's not me.
As I believed based on the observed data -- always follow the data -- this was not a power issue. As mentioned a few times power was logged and power headroom was double the amount required. Peak load did not correlate to the loss of connectivity for a device, or time, or temperature. Also, Windows believes the devices are connected, and no events are logged by any related device driver or windows subsystem.
The only correlation I observed was the apparent loss of communication (only for one of the USB 2.0 devices) would occur eventually when one or more USB 2.0 devices were plugged into the USB 3.0 HUB on the back of the mount while the USB 3.0 imaging camera is also plugged into that HUB. USB 2.0 devices in question are a USB powered ZWO EFW, and a separately powered Pegasus Astro focuser.
The errant behavior has not been observed over several nights since changing to the following configuration: plug the two USB 2.0 devices to the USB 2.0 HUB on the ZWO camera, and plug only USB 3.0 devices (imaging camera and ZWO guide camera) into the mount's HUB. Also, works fine bypassing the mount HUB completely. It isn't the devices per se. It is not the cables.
The problem will generally reveal itself in <6 hours by plugging one or the other of the USB 2.0 devices in to the USB 3.0 HUB alongside the USB 3.0 camera.
There may be issue with the USB implementation in either the mount or one or more of the attached devices. This is unlikely to be iOptron's fault and more likely a USB chipset issue somewhere, possibly not in the mount's HUB.
Another possibility is EMI from the cables (all top quality and with ferrites) causing odd behavior.
I've seen odd behavior and compatibility issues in USB 3.x chipsets and 2.x backwards compatibility. Some of it may even be USB 2.x chipset implementations. The original ASI120MM is one example. I bought my first one in ~2013. It always worked well under Windows and linux. Now it won't function properly with modern USB 3.x chipsets even with revised drivers. It appears to be a hardware problem that ZWO so far has not addressed even in revised drivers. New ASI120MM cameras work fine.
Anyway, problem apparently solved for now.
I do the same thing with USB and power (from my 12V battery into the saddle power port powered by the RA, then I have a USB 3.0 hub (with a USB 2.0 cable out the back) into the unpowered USB port (all power comes from the power port)
Only had one night so far and no disconnects. Hopefully we will get some clear nights with no smoke this week
Edited by DesertCrawler, 29 August 2021 - 05:36 PM.