Hi BSA,
Note that to state the tilting of the rear wheel, you should only apply the front brake and push quite hard on the pedal.
But I agree, I should take it apart to understand what’s really happening. I will simultaneaously change the freewheel which is wearing quite fast: the teeth of the pulley are still OK, but the pawls don’t engage well and the bearing shows a lateral play of about 1 mm…