Server list not working

[EOS]

Hello, my friend has a problem with the server list. When he enters there he writes the following message:
download error (status: 520): Failed to parse JSON. Unrecognized character(s) on ?:1

Also, when he comes to me via a Steam connection, that is, he joins as a friend, he starts an unstable connection to my server, that is, the connection is intermittently lost, the ping is high. And his Internet is stable 50 Mb / s. I had the same error that I described above, but I no longer remember how I fixed it. I just can't play with my friend for more than half a year./

[Loewchen]

See 99521. Keep in mind that his hardware is way below minimum specs, so if he can run the game at all he will likely drop from the server for being too slow.