Turbo3, you, sir are absolutely correct! I have confirmed that by going into
Settings/Privacy/Location Services/Leafspy on my iPhone 8
"Allow Location Access" to be set to "While using the App" (i.e ticked)
we successfully start distance/elevation displaying again (the Elevation and Speed are displayed at the top of the Graphs screen, and the graphing works when you start moving)!
This must have happened when I upgraded IOS to 11.2.6 just before I also updated Leafspy to v1.7.34 (I noticed I had an IOS update waiting to be done, so I did the IOS update first).
Note however, that the problem was also evident on another iPhone 6 that was still at IOS 11.1.2. When I upgraded Leafspy to 1.7.34 on that device, perhaps it defaulted the "Allow Location Access" setting to 'Never'?
Anyway, thanks again for assisting to get this sorted.
PS: Happy to help test new releases, but I guess I would still need to be enabled to access "TestFlight"!?