I’ve had the same issue and support says the IRS due to poor connection. I too use other virtual trainers and none have this issue. Also, support says the app will auto retry sending the data in 20 mins - I’ve yet to see that be successful!
I’ve resorted to loading the file to Stava manually. If you go to the support page on the VirtuGo site it will list where the “.fit” file is stored. Simply load that to Stava and you should be good.
Be sure to report this to tech support so they’ll fix it.