Sorry cant help too much there guess its because… software! 
Tried multiple ways but didnt seem to carry settings so could only get back online after a full reset at which point GW started with default EU settings for V3 - in line with last attempt, and is now happily online and appears stable.
Looks like @rharte came to same conclusion yesterday
https://www.thethingsnetwork.org/forum/t/running-into-problems-migrating-dragino-lps8-to-v3/52474
Atleast anyone following behind us now has a potential solution until Dragino fix settings carry forward for future updates. Am sticking with UDP for now inline with @wolfp 's comments in the other thread also.