Shared Album Photos Showing Up on Personal Photos Feed

I am seeing the wrong photos in my Photos section in Photos.app on iOS 13. My normal workflow is to put all of my photos into Photos.app on macOS Catalina, and then regularly sync a subset of my photos inventory to the iPhone. My wife and I also use a couple of Shared Albums to share photos with one another without polluting each other's Camera Roll (now called "Recents"). Note that in the Photos settings, neither of us are using "iCloud Photos" to upload our inventory of photos, nor are we using "My Photo Stream".

The problem started after macOS Catalina and iOS 13 were released. My wife and I upgraded both of our iPhones to iOS 13, and our iMac to Catalina. Not long after, she uploaded several wedding photos to a Shared Album in Photos. I could see these photos in the Shared Albums folder on both the iMac's Photos.app and my iPhone's Photos.app. After syncing my iPhone to the iMac, the same wedding photos now show up unexpectedly in the Photos section (as well as the expected Shared Albums section) on my iPhone, even though they are not in the Photos section on the iMac. These wedding photos are not in the Recents section on the iPhone, and are therefore not able to be deleted from the iPhone directly.

Other photos in the Shared Albums that existed prior to iOS 13 and Catalina do not sync to my main iOS Photos listing as expected. I have tried multiple corrective scenarios to no avail, including:

• Upgrading both iPhones to iOS 13.2
• Upgrading the iMac to macOS Catalina 15.1
• Turning off the Photos sync to the iPhone altogether, syncing, and then turning the Photos sync back on and syncing again

I am wondering if someone else has experienced this same issue since upgrading to Catalina and iOS 13. I also wondering if this is related to the known, current Catalina bug where photos in folders do not sync properly between Mac and iPhone.