Hello,
I had the same issue with your friend in the past. I couldnt even enter the server because everytime I logged in, always got kicked with unreliable connection reason. So from my experience if your friend's network is good enough and the computer can really run the game well, I'd suggest you to make sure whether the drivers are fine or not. Since I had this issues twice caused by the drivers. My first case was caused by a processor driver when I checked the Device Manager there was a warning sign. I remembered that I just updated the drivers manually few days before, then I rolled-back it to previous version and my issue solved.
My second case was about months ago, the same case caused by driver issue, but this time it was caused by my GPU driver (my GPU is AMD radeon). No warning signs in Device Manager, but I knew this happened after I updated the GPU driver with the latest version (it was optional release), I realized that the driver had some bugs so I tried to uninstall it and back to the older version (recommended release (WHQL)), after that I can play on TMP again. I hope this will help you & you friend ☺