Mac crashes when I plug in display 10.13.3

I have a non retina 13 MBP. (min 2012) and I've not plugged it into my ultrawide screen (Asus PB298Q) for some time but every time I have this week it has resulted in a catastrophic crash. I'm using a thunderbolt to displayport cable. My screen dims when I plug it in and it goes black with only the menu bar visible.

I hear hard drive activity but the machine does not respond at all not even once I unplug the display so I have to hold the power button down for several seconds.

On reboot I've have multiple issues with the hard drive where it's not recognised so I have to boot into recovery mode. Sometimes rebooting from recovery solves the issue. In some cases I get the prohibited icon on boot instead of the recovery.

Whatever hard drive activity is happening when it crashes seems to be having an effect.

I imagine this relates to a recent software update. I'm running 10.13.3