At what point are you both getting this error? (Is it after installation, before, upon launch, after launch, during linking?)
Could you both set up cases on our support site and upload screenshots showing the error in question, and your Epic Library.
Once you have done this, can you please let us know your case number so we can look deeper into this.
I'm sorry to hear that the TTS for Rainbow Six: Siege is not shown in your games library anymore.
I can confirm that the TTS will only be visible during active TTS phases. Therefore you should be able to see and access the TTS as soon as a new test phase starts.
Log files are located in the installation directorey of Uplay, in a folder called "Logs"
I'd also recommend running through this short guide to see if this helps.
Some players report that having software running that uses overlays cause issues with their mouse.
Please disable all background applications / deactive Discord and any other programs using an overlay.
Once this is done, can you test it, and let us know if there is any improvement.
It could be using your mouse on a smooth wood surface.
My desk isn't shiny, but it's an absolute nightmare to use a mouse without a mouse mat :/
It could also be worth going through this guide to make sure everything is up to date and to make sure the utilities you have running in the background are not causing this.
If you encounter players like this, feel free to report them from directly in game.
When reported, we can then conduct an investigation into their behaviour.