Random Camera Roll Photos not being deleted after Mac Photos Import

I've been experiencing an odd new issue with Photos that I haven't managed to find any mention about online

When importing photographs from my iPhone X into the Photo app on my MacBook Pro I've always selected the 'Delete items after import' check box. For years this worked flawlessly and cleared all imported photos, but recently the function seems to have become intermittently faulty. With no obvious reason, and only every few imports, some Photos are not being deleted from the Camera Roll on the iPhone. I import my photographs frequently so have noticed it's always a continuous string of photographs (not random photos from amongst).

I've even upgraded my MacBook Pro to a new model whilst experiencing this issue and the same problem occurs on both laptops.

I've attached a photo that should show even better what I mean. As you'll see the 'Delete items after import' check box is ticked, as it always is (I check it every time). However, the photos that are showing as 'Already Imported (7 photos)' shouldn't exist in my iPhone X camera roll as they should have been deleted in the previous import procedure.

I can't seem to find a fix for this issue. Help would be appreciated.