Spent some more time on it this morning. Rewriting to capture steps more clearly
I have had three devices in this location -
KPL #1 - Orig KPL (when KPL first came out, years old)
KPL #2 - Dual Band KPL (about a month old)
KPL #3 - Replacement Dual Band KPL (same firmware rev as KPL #2)
KPL #1 died no lights, no nothing and was replaced. Replacement procedure was to put in KPL #2, do a full reset, and replace device with ISY.
KPL #2 worked for a few weeks.
PLM died (ISY reported safe mode). Replaced Dual Band ISY with old single band one (ordered new dual band). All was working for a few days...
KPL #2 stopped working - wouldn't communicate with anything, not even ISY. Did factory reset. It would communicate with ISY. Did restore device from ISY and it wouldn't control or respond to any other switches. Installed KPL #3 with "replace device in ISY".
KPL #3 wouldn't communicate with anything except ISY either. Tried factory reset and replace device. Didn't try to manually link it to anything. Deleted the device from ISY and added all the links back manually.
So, now everything is working again and this is where I sent my initial post of this thread.
This morning I took KPL #2, did a factory reset, added to ISY, and started adding links and it is working fine.
So I have to assume somewhere along the lines (either moving from single to dual band KPL or when the PLM was dying) the programming of the KPL was corrupted and kept getting written back corrupted into the KPL when I tried to restore device from the ISY.