[Zubersoft]

These kinds of problems can be very difficult to analyze. I have switched through several routers in my house over the years, but none of them have created any connection problems between my tablets and the companion app running on my PC. So it's really hard to say whether the problems you are seeing are caused by something to do with the tablet, the Freebox V6, or the PC running the companion app. Let me ask this - have you tried just creating the library backup file on the tablet itself by opening MobileSheetsPro, tapping the three dots at the top right and then Settings->Backup and Restore->Backup Library? If the backup is smaller than 4 GB, this should work without any issues, and then you can just transfer the .msb file to your PC using a USB cable or you can upload it to the cloud.

Mike