So to continue the experiment, I created a new collection on each of the devices I have:
- iPhone
- iPad Air
- iPad Pro
- PW4
- Moto G
- Voyage #1
- Kindle 8 gen
- Voyage #2
The first five of these are synced. The Moto G tries, but shows only 9 of the 12 collections, unaware of the 3 oldest ones, poor thing.
But the Voyage #2 collection never shows up on the other devices, and both it and the Kindle 8th gen never sync to the ‘current’ set of collections.
I Reset both and at least for now they have re-joined the fold.
Overall it is a better situation than it seemed at first. Some of the synching takes awhile. But it does seem there are situations that require a Re-register or Reset to correct.