Fit files created by simulator no longer able to be converted to csv using FitCSVTool.jar

I am using SDK 3.1.7 and FitSDKRelease_21.22.00.

I run the simulator and create some data using Simulation->FIT Data->Simulate Data.  After running this I select Stop and then select 'Save FIT session' which asks me for a filename etc.

In the past I could then convert the FIT file into a csv by running:

java -jar /.../FitSDKRelease_<nn_nn_nn>/java/FitCSVTool.jar -b <file>.fit <file>.csv

but this is now returning the following error:

FIT CSV Tool - Protocol 2.0 Profile 21.22 Release
Exception in thread "main" java.lang.RuntimeException: com.garmin.fit.FitRuntimeException: FIT decode error: File is not FIT format.  Check file header data type. Error at byte: 24
    at com.garmin.fit.csv.CSVTool.run(CSVTool.java:246)
    at com.garmin.fit.csv.CSVTool.main(CSVTool.java:332)
Caused by: com.garmin.fit.FitRuntimeException: FIT decode error: File is not FIT format.  Check file header data type. Error at byte: 24

I am using macOS Mojave v.10.14.6