Any news? Will try to explain in more detail.

There are two types of cs 1.6 server query:
1) Old p47 GoldSrc format - "details" (deprecated on p48)
2) Modern p48 Source format - A2S_INFO

AFAIK gametracker uses Source type request. The server can answer three ways, depending on the ServerInfoAnswerType option:
1) p47/48 server: 'GoldSrc answer' + 'Source answer'. They will be received in separate packets.
2) p48 server: only 'Source answer'.
3) p47 server: no answer.

The problem relates to the second type of answer. Seems when gametracker sends A2S_INFO he is waiting for 'GoldSrc answer' instead of 'Source answer'.