I ran into one problem with my Mach3 license not working after doing a clean install of Windows 10, which I managed to fix.
I had installed Windows 10 on a new second hand PC (a Dell OptiPlex 755) I am using for my CNC controller using an ESS SmoothStepper board. However during the Windows 10 setup, I used my Microsoft account as a login. This caused the Windows 10 install to abbreviate my email address as my Windows username (folder name). My Mache3 license didn't work.
So I did a complete Windows 10 reinstall (no big deal as I stuffed up a few other things - considered it a practice run), however this time I skipped the Microsoft sign-in and instead created a local user account with my full name (as it appeared in my Mach3 license), which created a matching folder name. This time when I reinstalled Mach3 and copied over the Mach1Lic.dat license file into C:/Mach3, it worked.
Something to watch out for if you go this route. Other than that Windows 10 appears to run all my existing CNC software and drivers just fine, GWizard, CamBam, MeshCam, CutViewer, Mach3, ShuttlePro.dll etc.