Thanks for all your replies and listening my tale of woe
I can report partial success. Spoke to Garmin support yesterday and went through the various issues I experienced last week.
They repeated the various suggestions raised on this forum
- Factory reset incl delete user data
- reinstall maps ( this takes around 30 mins)
- Convert your routes to TCX as these have a they will have a queue sheet for turns. Note you can do this via https://www.gpsies.com/convert.do?language=en
They also noted that my Garmin has had a few owners which made them suspicious.
Tested earlier this evening and initially kept recalculating as I cycled. Then it performed a longer recalculation ( took about 2 mins) thereafter , I started seeing turn by turn prompts : right,left turns and also road names ( Til now was as rare as England winning a game on penalties