Hi Stephan, on Squeak with two monitors, while I don't see the Vm lock up (one can still see the clock ticking in the menu bar), I do see the image become completely unresponsive to mouse input. So I see a serious problem with the latest Squeak VM too (I tested a 64-bit system on a home built VM derived from Croquet Closure Cog[Spur] VM [CoInterpreterPrimitives VMMaker.oscog-eem.2530] 5.0.201902020720, with older platform code, avoiding Ronie's latest Metal shader code which doesn't compile on my 10.13.6 MPB).