This isn't an issue with the FulGaz ride data or FIT file, rather that the training software you are uploading the ride to (eg: Training Peaks or Garmin Connect) is being "tricked" into thinking your ride took place in the actual location of the virtual ride, rather than in your own time zone.
Depending on where your virtual ride was, this could mean it appears on the incorrect day. Strava works this out and corrects to your own time zone, whereas Garmin sometimes does not.
To solve the problem, you can drag and drop the session to the correct day, please click here for details on how to move activities on your Training Peaks calendar.
You can also use software such as Fit File Tools to edit the time stamp in the FIT file.
It is also worth double-checking your time zone settings in those training apps, just to ensure they are still set to your own time zone.