Thanks for the reply. Yes, my watch and iPhone are up to date with the latest OS and have been since their publication. I noted today that for three days in a row, a workout has been transferred to the Fitness app but the Map/track/GPS data still remains absent.
(As an aside, I have also noticed that the Sleep app does not record all my sleep but it's not just the Apple Sleep app that doesn't ... also Pillow hasn't for weeks. I have checked all Settings, or at least the ones I know about, to make sure that automatic collection of data is activated but still some Sleep data is missing or not there at all for days.)
I followed the instructions above and reset the calibration data. I will check if there is any change following my next workout.