Many thanks for your responses. Problem has been solved.
Community folder had 75 items which I had saved previously. I then transferred to the new install of MSFS.
Decided to remove all items from the Community folder and then reintroduced 18 at a time. Of course the last 3 were placed back in the folder. Started MSFS and the problem returned.
Since it appeared to be graphic related problem I removed zinertek-misc-enhanced-airport-graphics-v2-0-0 which had not caused a problem previously. With that item removed problem disappeared and has not returned on approx 10 restarts of MSFS.
Will try update to Zinertek Ver 2.5 when time permits to see if problem again presents.