Hi Chelidon....





So the exact same things were happening for you... constant hanging blank black screen... where my cursor would jump from the middle of the screen or wherever I would have last placed it and move to the top left-hand corner of the screen and just hang there.... the longest I left it was 3 hours.





Also.... after attempting the Security Update 2018-002 I could never shut down my MacPro normally either on the scheduled Energy Saver settings or my the using the Finder/File/Shutdown menu... the only thing that works is a hard press Power OFF.... ? Did that happen for you..?





Also... any attempt to re-install the HIgh Sierra macOS or upgrade to the new macOS Mojave where halted also... as they required a shutdown to begin the install process and that again was not possible. Did that happen for you..?





If you experienced all of the above and your Terminal commands helped then I would really consider your option.... it's just that I never ever really use Terminal for anything... so I'm just very nervous to try it.... unless I know for sure it fixed my exact same issue for other people, which it looks like it has for you.





Thank you again Chelidon for all your help and assistance with this issue... 🙂