I have used my nMP (D500, 32GB) for few years with various issues every now and then; notably resume from standby crashes GPU so I don't. Currently I use two displays, Acer HK321 and Dell UP3214Q (both 4k). With 10.13.5 there seems to be a new interesting issue; if I connect one of my displays via HDMI (and I should, as there is no 4k output over thunderbolt in login screen?), the screen goes black every few seconds, and sometimes re-syncs again and sometimes now. This makes that display unusable via HDMI. Same display is still fine over thunderbolt (aka mini displayport), and the behavior started with 10.13.5, so I suspect that is the culprit. I guess I will have to try the HDMI cable with different computer to be sure, but I am very surprised if it broke down just as I upgraded to 10.13.5. I wonder if I should just downgrade the AMD drivers or revert to a TM backup, this is somewhat .. annoying.