> I did one further check today, and by changing from
> where d.diagnosis starting '206', to
> where d.diagnosis between '2060' and '2069', the plan changed to

what

> I would have expected it to be in the first place.

Yes had the same problem a while ago. FB doesn't like Starting in
combination with combined key fields. Using between instead fixes the
problem.

Greetings,
Filip Moons