Thanks to the help of the community we have been able to identify an issue concerning custom tracks in My Workouts processing and never successfully completing.
It appears that the processor that we use will change the decimal separator depending on the language set on your PC (not the language set within BoxVR).
To clarify, the decimal separator that will successfully complete processing is this: '.'
The decimal separator that will cause never-ending processing is this: ','
Since this depends on your language set in your PC settings, please refer to this wiki to determine if you may be affected and if temporarily changing your language will help:
We hope to have a fix deployed for this at some point soon. Thank you for your patience.