I had similar inconsistent results on UM16.04 and now UM18.04b2,
I’m using the “Traditional” desktop
I opened the “photos” on the iPhone firstly.
I plugged my iPhone 6S+ ((iOS 11.3) into the USB port.
The iPhone responded with a tone and the note “Do you trust this computer”
I do and entered my Phone password.
Meanwhile my screen on the UM18.04b2 displayed the Camera icon and the text “iphone”.Two windows also appeared on the UM18.04b2 desktop.
"Unable to mount Documents on “Name of iPhone” Unhandled lockdown error (-2)(I hadn’t Trusted the Computer yet)
and The "Choose Application " handler window. I selected the “Open folders” option.
I created new folders on my desktop for each of the Apple photo folders( Apple100 …etc.) .
I opened each Apple folder on the iPhone and “selected all” and dragged them to the respective folder .
I unmounted the iPhone and to confirm.
UM18.04b2 did not even recognize (nothing in the device window eith swo nothing to mount)the iPhone !!
Tried once more on a different USB port.
The desktop recognized the iPhone and TWO iPhone icons appeared. One showed the Camera icon and the other was something that looked like a cell phone with the text below "Document on xxxx iPhone A window opened and showed some random iPhone Apps. and the photo folders.
This is the last major issue I have before pulling the plug on Win7.
Another loosely elated issue appeared. I can’t rename folders on the desktop with the iPhone mounted. LOL
Sorry to be so wordy. NOOBI