Syncing photos with iCloud STILL stupidly slow with iOS 26

This started with an update some time ago... syncing ONE photo to iCloud, over wifi with an excellent connection, into masses of storage space. The phone just sits there with the Photos app saying "Syncing 1 item..." when it is clearly doing nothing. Currently nearing 30 minutes.

This is from a gen 3 iPhone SE running iOS 26.0 although it was happening with the previous version as well.

The twist though is that I also have a gen 2 iPhone SE running iOS 26.0, and that syncs photos immediately and always has done.

The two phones have identical apps installed and identical settings as far as I can see. They are connected to the same wifi and are on the same 4G network with the same provider.

Intelligent suggestions as to why this might be happening welcome, presumably there is some obscure setting hidden amongst the bazillion settings iOS is now swamped with that I have missed.