Servers with more than ~ 125 players show that there are 0 players connected:
Proof:
https://i.gyazo.com/39007bcf382e0ba6a9060e317702c7ac.png
According to steam protocol, the number of player is encoded in a byte (0 - 255).
So i guess that you store the result of the request in a signed char (-128 - 127) so servers with more than 127 players show 0 players.
https://developer.valvesoftware.com/wiki/Server_queries#Response_Format_2
Gametracker is able to show the real number of players so the problem is not in the reply but in the way you display the result.
Thank you {F27183}