That was my point, task 2 can not move ahead even though task 1 still has 2 days slack. As a result, the critical path filter won't show task 1 and any critical path tasks before task1. The whole project shows task 2 as the only one task in the critical path, that's it.

The early/late start/finish date calculation for the slack doesn't work under 2 different calendars. May be it should be based on the more restrictive calendars between the two task? Any article discuss this special case? Need advice on the alternatives in MS Project?

BTW, what is FNLT?