Thanks for pointing me toward a line of inquiry. I’ve got 28 tasks in this composite project which lack dependencies. Eight of them have total slack of 0, the rest are non-zero or non-zero with a question mark because the duration is not yet determined. Only 3, all from the same sub-project, are being drawn red (critical), the rest are blue. In fact every task without dependencies from that sub-project are critical.
I’ll puzzle on this some more but you’ve given me something to chew on.