Troubleshooting...
1) Free'd up 150GB of storage space on the iPad Pro - so there's plenty of room for 112 photos using less than 3GB!
2) Deleted the 112 photos in the "problem" Album from Photos on Mac.
3) Confirmed 112 photos and album are no longer visible in iCloud.
4) Confirmed 112 photos and album are no longer visible on iDevices.
5) Closed & Opened Photos app on Mac.
6) Re-imported the 112 photos back into Photos app on Mac > created new Album with 112 photos.
7) Closed Photos app on Mac.
8) Confirmed 112 photos and new album are visible on iCloud / iPhone.
Back to the iPad Pro & new album is visible and shows as containing 112 photos, but only first 9 and last 9 photos show up!
Help someone please.
As an aside - iOS 12 & 13 updates have been nothing but a pain! Far worse than usual.