Did more tests and the results look completely random. I get zero rating on a couple of pictures in one test, while I DO get ratings on the SAME pictures in a following test.
Not sure yet on the amount of pictures involved in the sync. My biggest tests were done with aprox. 1200 pics. None of those went well.
I'm now running a sync test on aprox. 250 pics and interestingly enough the first two shots did NOT get rating (while they do have rating on the desktop), the next 7 did get the rating synced, and from that on NO rating is synced (while the original shots DO have rating). Confirmed on both LR Mobile on iPad and the web version of LR.
This looks like LR desktop is doing stuff randomly, or uses a set of unintended rules that are still too deep for me to figure out.
Any way, Adobe, all of this is not impressive. And I'm being polite here.
Robert