maybe it was construction-related, if the intercom worked I might've been able to hear what the conductor was trying to say about it instead of a garbled static version of the teacher's voice in charlie brown

This is much more common on the LIRR or NJ Transit than the subway. Certain stations only allow the first 10 cars, last four cars, etc

The old South Ferry station used to be like this, otherwise I can't remember of any others.