I encountered the following problem when using Team Viewer.
If I start a FTP transfer remotely the speed if very slow - 20kB/s. Even if I am still connected through Team Viewer but I start the transfer from the computer, the speed is normal (10MB/s).
First time I come across this bug was almost two months ago. This happens for both Team Viewer for Windows and for Android. I have the latest versions installed and Windows 10 with the latest updates.
I checked this behavior using Total Commander and FileZilla on different computers with the same result.