Ok, so there are a few variables here. For me personally if I switch off WiFi and mobile data when outside and take landscape photos, they save to the phone and can be edited on the phone there and then without issue. When back on WiFi the images upload to the cloud.
However if data is on when outside and you have the new photo styles on, and the connection maybe be limited - there is a lot of data to be uploaded to the cloud where the edits / saves would occur.
This occasionally means the image is ‘stuck’ between the cloud and the device so any edit / save cannot complete.
Usually when back on WiFi - and a reboot of the phone - will resolve the issue. There are also some reported work-arounds where you can create a copy of the image and work on that. The copy being on the iPhone.
I haven’t had any issues since my reported one above.