USB Connection / Read Error on iPhone

Aargh, same old problems again. New iPhone, iOS 11.3 all up to date,  no problems for a while (thought I had seen the back of the gremlins with my old phone, but I have a 50% success rate in getting my S3 to read the iPhone. It is random.  Usual USB Connection Error / Non Read. Have cleaned out all ports. Switched plethora of working official cables. There seems to be a definite software problem between iOS and Smartlink - prior to the main iOS upgrade last year there was no issue judging from various other posts.

Would welcome any suggestions, and yes, I have performed hard resets of both phone and the S3 unit and closed all other apps, and waited for a while to connect and tried plugging in from cold and letting phone boot up from insertion of USB - all to no avail. 

Go to Garage? Headunit update?