iPhone opens photo app on iMac but goes into a loop of being recognised
when I connect my iPhone 7+ 14.2 to my iMac Catalina I OFTEN - but not always- get stuck in a loop where the app recognises the phone & say preparing to download photos & the iMac charges my phone but then the charging stops and the phone is no longer recognised by photos app. This repeats continually every second. I have tried all the usual ideas - changing USB port & restarting the mac. Once it starts looping I have only one alternative : Unplug the phone. Any ideas ?
iMac 27″, macOS 10.15