UPDATE:Looks like your Ethernet port on the OP2 panel is "constipated". Have you tried the following
A - disconnect the Ethernet port, reboot and only utilize your serial connections to the panel. Your serial devices will not hiccup and your time will stay stable with no Ethernet connectivity (if it is an Ethernet issue).
(busy week at work and I hadn't gotten updates to the thread but thank you again for everyone who's contributed time/attention/ideas!)
Okay, so the short version free of hysteria (and the past couple weeks have been full of hysteria!) is that I started with @pete_c comment above and just as suddenly as everything fell apart, things slowly started working again!
- I have been able to connect via Ethernet AND maintain a persistent connection for days.
- I have been able to download the entire .pca file at once and the connection has maintained.
- The OPII serial ports didn't work for a few days: #1 (VRCOP Z-wave) worked, but #2 (HiFi2) and #3 (URTSII) didn't work at all for a few days and then suddenly started to work.
- I've noted that my OMNISTAT2 has "reset" a few times - the backlight setting keeps getting reset to the default but otherwise everything seems okay.
- I've lost date/time settings on the keypad consoles a couple times.
- I'm still getting "clusters" of SYSTEM RESET errors in the PCA log file. 6-8 at a time all together but at random times and I cannot see any pattern.
So there still seem to be some lurking problems, but as a simple fact my system is otherwise up-and-running and everything seems functional. I have reconnected all of my iPads running Myro:Home and each has maintained a connection, shown proper statuses/refresh, all functions work - including (my most important feature) CCTV camera "pops" triggering on each screen where motion is detected.
I cannot by any means say I feel comforted that whatever happened is "solved" because aside from the intentional reboot sans Ethernet cable, nothing else is changed. And if all of this was caused by my OPII Ethernet port being "constipated"... well, I have no words for that.
My plan is to keep running "as-is" for another period of time (week or two?) and report back on what I'm noting, as I did above. I'm so grateful to be back from the Stone Age, but quite traumatized by the experience (#FirstWorldProblems, right?) because I don't feel settled on what happened and why. I don't ever want to go through this again!
Trauma aside, after my "settling period" above, I'll go back through the very helpful notes/recommendations and get to the very strong advice to "wall" the OPII behind a "lesser/slower" segment of the LAN. Again, @pete_c thank you for the history links. As of now I know how to throttle-down the port to a 10Mbps half-duplex speed, and I started to tinker with the "storm control" bits lightly but that's about where my networking knowledge ends. I'll invest the time to understand the steps shared before I come back with questions on that, and hopeful that might solve the issue more permanently. I still can't believe a noisy Ethernet port could bring down the whole shebang so hard!
So so grateful for how generous you guys are with your time and experience and expertise, THANK YOU! I'll update again soon...