iPad to iTunes syncing issue on a iMac

I have an iPad air running iOS 11.2. iMac running High Sierra 10.13.2 and iTunes running Version 12.7.2.58 although I have this issue for awhile. When I go to sync my iPad it connects, then disconnects itself and then reconnects in a endless cycle. I have tried various cables, which do not make a difference and those same cables work just fine in a regular charger. This just happened when I'm plugged into my iMac. I've used both Apple brand and 3rd party cables, same issue. This issue also occasionally affects my iPhone 6s+/

I've rebooted the iPad and iMac, but that doesn't make a difference. I was able to sync via WiFi, but since that last High Sierra update, that's doesn't work as iTunes seems to have "forgotten" my iPad exists.

Ideas anyone?