I've noticed that you also tried 3D acceleration and full-screen mode, which provided me with a new idea. Please do the following:
First copy the current Win 7 to 10.vbox file, to post it later on. Then start the VM, switch to full-screen mode, power off the VM, start it again, so that it only uses well-known resolutions and full-screen mode. Post a zip file containing the Win 7 to 10.vbox file copied earlier and the new VBox.log file.