So been successful using my laptops and Samsung tablets no issue.
Yesterday one Dell refused to connect, today the other and now not even the Samsung Tab via DeX, which even says it is connected to an external display.
I have a Thunderbolt 3 and USB C 3.1 worked fine now neither work.
Someone mentioned they have to do the following a few times a day, power off monitor, unplug wait, also unplug USB, then power up, which did not work for me.