Agent when doing net.tcp.port[] to a non-responding port, waits for Timeout from it's config, default = 3.
Server, when asking passive agent for such check, waits for Timeout from it's config, default is also 3.

This leads to effect, that in installation with default timeout values server will never get reply for the item, if net.tcp.port[] is checking a non-responding port.

Simular probably is with net.tcp.service[] and may be some other items?