H Kirk.
With regard to the 'Sync' collection you asked about, both the original collection and the 'Sync' collection show off-line.
Now a complete mystery. I have changed my workflow to this - all catalogs are now stored on my iMac and MacBook HD's as separate items of course. I use a proprietary syncing app to update to Google Drive after PM+ is closed. On my MacBook I use the same transfer system now i.e. sync to HD when PM+ closed then use the catalogs from the HDD BUT all of the catalogs are now ON-LINE on my MacBook to the NAS?
i.e. although the catalogs show off-line on the iMac they show as on-line on the MacBook without anything being altered before transfer.
Both iMac and MacBook are running the same OS version and the same PM+ version.
This of course is pointing to a difference between the architecture of both systems, but please correct me if that's not feasible.
I'm sorry if this sounds tedious to you but it's now driving me crazy and I hope you may be able to shed some light on it.