Simulation>Fit Data > Simulate Data and Replay Fit File no longer working.

It was working till earlier this year, but I didn't get around to querying it then.

I notice there is some discussion around replaying Fit files, and wonder if it is connected.

I'm running SDK 3.1.7 on Mac Mojave 10.14.6 in Eclipse 2019-06 (4.12.0).

I have tried running under earlier SDK's (back to 3.0.12) but still no joy.

It won't replay Fit files either: no error, just no callback to function GPSData() from 

Position.enableLocationEvents(Position.LOCATION_CONTINUOUS, method(:GPSData));

I upgraded Mac from HighSierra to Mojave around the time it started to fail, so I wonder if that's connected.

[EDIT]

Just updated to Mac Catalina 10.15.3 and still no Simulate Data