After the many months of chasing a solution to this I can report that I bought a new Banana Pi R3 and everything works as expected.
I wish to thank all the people who tirelessly trie stoa assist me.
As I bought three USB - UART adapters and tried every known combination I concluded the UART circuitry failed on the first R3. A R3 confirms this as far as I can see. Thanks again for all the help.