@Heino76 recently TP-Link release a firmware update addressing this issue. I've updated my Decos and I will keep an eye on it the coming days.

@Heino76 so it seams it's Microsoft related hahahha

@Heino76 I still have the problem. It seams that I only have issues when my Microsoft Surface laptop connects to the main deco. When I initially connect to another Deco than the main one I never had...

@ReallyHopeful I am almost at the point that I will return it to the shop. Might be an idea for you as well.

@Sjek You could set the KPN router in bridge mode I would expect. Nevertheless you would expect it to be stable in every mode.....

@Sjek while running it in router mode?