missing photo albums on iPhone after iTunes sync

I use iTunes and a USB cable to sync select photos between my iMac and family phones. All devices are running newest OS versions.

Most photos and albums appear to synchronize without difficulty, but I notice that at least one album is missing from the list of "My Albums" on one iPhone. However, if I use the search function in the photos app on the phone, it finds the album on the phone as well as all the pictures. This problem is currently noticeable on only one of our two phones. I am not syncing exactly the same albums to each phone.

iMac running OS 10.13.13 with iTunes12.7.3.46

iPhone 7 running iOS 11.2.6 -- problem not present, all albums appear in "My Albums"

iPhone 6S running iOS 11.2.6 -- at least one album missing from "My Albums"

What I have tried so far:

• Repeating the sync.
• Repeating the sync with a different USB cable.
• Restarting both iMac and iPhone and then repeating the sync.

Can you suggest any other approach to resolving this problem? Is there any limit on the number of albums in "My Albums" on the iPhone?

Any additional information or suggestions would be appreciated. A similar question was posted in Sept. 2017: missing photo album name after iTunes syncmissing photo album name after iTunes syncmissing photo album name after iTunes sync