Task 2 has a 5-day duration, is tied to Task 1 with a predecessor, and...

The primary assignee had already submitted a Commit Date for the previous planned start date on Task 2, even though the project owner did not accept this Commit Date, the project plan made this date a Must Start On Constraint on Task 2.

The project owner has at some point made a manual change to the planned start date of Task 2, which has in turn changed the Task Constraint of Task 2 to Must Start On.

The primary assignee had scheduled time off during the new planned start date that Task 2 should have shifted toward. Due to this time off scheduled the date remained the same.

The project owner has at some point made a manual change to the Task Constraint of Task 2 to As Soon As Possible, which has forced the date of Task 2 to be static.