Your comments

I am happy to report that turning of my iPhone and restarting it seems to have solved the problem. The App is being very well behaved now. :-)

Thank you for your help, Amber.

-- Tom.
Thank you for your prompt reply, Amber. I fully expected time zones to mean no reply until at least the next day (I am in Australia).

I will try turning off my iPhone and restarting it (which I can’t do at the moment because it is involved in a procedure that I cannot easily interrupt) and let you know the result.

The question of whether I use the desktop app or the browser has hardly arisen as the app on the iPhone has always quit before I get to the stage of launching either app on my Mac. As it happened, I only wanted to transfer two photos but I couldn’t even get to the stage of selecting them before the app quit.

I will let you know progress in the next 24 hours or so.

Thank you,

-- Tom.