I think it turned up in the November 2019 Update. It's not "supposed" to be on automatically but I don't recall turning mine on.... Anwway, all seems well now!

Tim, although the FSX database you supplied gave me a functioning G-Plan it didn't fix the user aircraft problem, so I carried on and have what I think is the definitive solution to this problem  (and possibly others with similar difficulties).

The answer seems to be the Controlled Folder Access feature in Windows 10.  ::)

With this feature on, I cannot build the database and the yellow user aircraft and breadcrumb flight path are not seen (even though the yellow wind arrow is). >:(

With the feature off it is possible to build the database and both the user aircraft and breadcrumb can be displayed. :D

It is also possible to have the feature on if the location of Plan-G.exe is included in "Add An Allowed App".  :)

I hope this helps folk.

That solved it!  :) :) :)
Many thanks for all your help, Tim.

Thanks Tim,

Here's another log file with slightly different content but still, I think, no clues. The failure pattern is still as in the first post of this thread.

I guess we'll have to put this down to "software, huh!" for the  time being and I'll keep trying to see if I can spot any more clues.

Thanks for your help.

Thanks for the thoughts, Tim but the paths seem OK. I'm not trying to build across a network.

Connection now working again....

Thanks for that I will explore the connections.
I deleted the log file and ran the test again here is the revised log file..

Since I updated to 3.2.2.167 Plan-G is no longer showing my position. I thought to rebuild the database but when I did so I get through to "Writing 30755 runways", the green bar moves all the way across and then the build process hangs (takes twenty minutes or more) with the message "Failed to build database (A duplicate value cannot be inserted into a unique index. [table name=Runways, Constraint name=PK_Runways])" I tried uninstalling and reinstalling Plan-G (and removing all the Plan-G files folder) but this hasn't made any difference. The log file doesn't seem to be capturing the problem (copy attached) - I ran my last test at around 11:50am and the log file shows no activity after 09:28. I'm running FS-X Acceleration on Windows 10. Any suggestions welcomed.