Maybe I should have spotted this before since there are so many questions about avrdude getsysnc on the forum....
There is a return value 'resp:0xZZ' that should give a clue to the problem.
Response i am seeing is:-
avrdude: stk500_getsync(): not in sync: resp=0x6d
Is there info anywhere on what 6D means?
I've looked at some avrdude files on Github but the're beyond me.
Is there more basic info anywhere else?