Jan, the AMOUNT of wind is not the issue. As you say it's still flyable. But perhaps there's something going on with the flying site you're using which causes some nasty rotors to form downwind of some building or geographic feature at this flying site. By any chance is there a grove of trees or a cliff located upwind from the spot where you mostly find you lose control? Is your flying field downwind on these days from a group of houses or other buildings?

The fact that you can pretty well go for some number of flights on other days without issue and on multiple airplanes and sets of gear says that it's not you, the gear or the models. And with some thinking about the conditions I bet you'll start to remember that there's more to this wind issue and wind direction coupled with the crashes than meets the eye. Did many or all of your loss of control moments occur in a fairly limited area during these particular wind conditions? I'm thinking that there is a link here since it seems to be the only common item you've brought to the discussion.