I reckon that this is a wake related issue as well.
This is because you are now experenced at assessing student competence and the student was consistent on all previous landings...The spanner in the works was that pesky 737
Of course with a student pilot getting them to start a stopwatch when the 737 rotates is an extra burden....
The assumption is that ATC will always ensure separation >3mins
- not neccesarily!
