Cinema display stopped working MacOS 10.14.4 upgrade



hoping someone might be able to give some advice or point me in the right direction to try to sort this out.

I have a Cinema Display 20in (Aluminium) connected to a 2018 Mac mini, using a DVI to HDMI adapter.

The display was working fine until I upgraded from 10.14.3 to 10.14.4 yesterday.

Now on starting the computer up, I get a snow storm after the computer boots from apple progress logo to login screen. If I unplug and plug the HDMI adapter the display returns to normal.

Can anyone help?

Many thanks,