Just to let anyone else affected know:
I got this fixed by simply turning off scaling, rebooting the Windows 10 host twice just to be sure, and then set my scaling to the original value.
I use a scaling of 150% in Windows (set in Settings > System > Display), which serves me well to get a decent screen real estate on my MacBook Pro 14'' Retina display, both if I boot Windows 10 natively using Boot Camp or in VMWare Fusion.
After the update I got a popup after booting, telling that the resolution got changed and that I have to log off and on again.
I can't recall the complete history but found the software to be more stubborn than myself, not letting me keep my preferred settings.
I got this finally resolved by turning scaling completely off and rebooting, which probably completed a task set by the installer.
After that I re-applied my custom scaling, and Fusions seems to be content with them.
Small Tip:
When using scaling, turning the High DPI scaling override on in a program's or program shortcut's Properties allows to correct the size of individual applications which don't scale (I use the "Application" setting for a few editing tools which appear far too small in my case).
Open Settings -> Display, if the checkbox "Automatically adjust user interface size in the virtual machine" is checked, the scaling in Win10 VM will be changed into 200% automatically. If you are going to use customized scaling settings, please uncheck it. Then you will never see the popup message that asks for a re-login.
I had unchecked this before the upgrade and it was still off afterwards. Maybe I was not clear enough in my post.
Hi,
In the same settings, "Full resolution for Mac Retina", can you uncheck that as well.
No, when you turn off "Use full resolution for Retina display" in VMWare Fusion > Virtual Machine > Settings, then you are not able to use the higher resolution for more on-screen real estate (smaller borders, icons, tiles, text etc.) in Windows.
I was specifically talking about the settings in Windows.