Good morning Patrick,
The 5 hubs in the machine seem to be all communicating happily now. It was definitely 'operator error' on my part, because once I had the IP's all configured it still wasn't working repeatably until...
I changed the host names of the hubs so they weren't all the default "hub5000". Oops.
Thanks again for your help with all of this and if I have a hint of trouble with them from here on out I'll go the usb route. Seems to be running happily now though.
This is all that came up in the log of the hub that does that 'flashing behavior:
2020-03-06T17:38:59 <ERROR> phidget22 :
****************************** Logging Enabled ******************************
* Phidget22 - Version 1.6 - Built Mar 6 2020 10:34:26 *
*******************************************************************************
This was taken as the device was connected to a temperature Phidget and it was 'flashing' in and out of existence. The temperature unit, not the entire hub. It remained connected.