Thanks Coach Dave and Grant for your replies. It makes a lot of sense what you say about making sure the timing of the kick stays in synch with hip rotation. I will keep in mind the count you mention for the 6-beat kick with one for each hip rotation and two on the edges. It doensn't sound easy, but worth a try!
I guess training with a kickboard does not make much sense, as the whole timing issue is missed and we kick on a flat position.
The frustrating part for me is being left behind in practice by other swimmers for whom kicking just seems natural.