It happens just the same to my rpi3. I’ve got a vero 4k+ and a rpi3 and both upgraded yesterday. Some issues with the network, ip manual reverted to dhcp and things like that, and with the audio (I had the old bluetooth hack around), but this thing with the hdmi is beyond my league. It won’t start mediacenter without a monitor plugged in, and it won’t let me in through ssh either. With a monitor at the start everything is fine, you can plug it out after the system is up.
Update: system starts fine, and other network services too. Mediacenter do not. When you try to ssh, a new session is open in osmc, but remote terminal won’t show promt, just freezes. Later today, I will try to see more.