I just updated my iMac (27 inch, late 2013) to Catalina. Now, when I connect my iPads, the charge icon on the iPad flashes on and off roughly every 2 seconds, and the charging 'bong' sound occurs also every couple of seconds. On My Mac the iPad appears and disappears in the finder with similar frequency. Sometimes the iPad flashes a 'trust this computer' message – but never long enough for it to be actioned.
I know the cable is OK and the iPad charge slot is not blocked because it charges just fine from a plug-in charger and it worked before the Catalina update. I have also tried several cables I know to be good – same problem with all.
This happens with 2 different iPads, but not my iPhone. All devices are updated to ios 13.1.3.
I have done a hard reset of the iPad and also a shut-down, unplug, replug and restart of the iMac – nothing helps. I have also tried different USB sockets on the iMac – again, no difference.
Thanks for your help.