Hi There,
I do know that on some Dell Screens you need to enable DP1.2 Mode manually in the settings of the screen because factory default that would be set to disable.
I have heard of MST Hubs needing a power recycle before screens showing a picture again, mainly after coming out of sleep mode on systems … not found a remedy for that yet. You should be able to just hit the reset button on the back of the hub and “normally” your setup should be back on track. 
I have not heard of a faulty MST Hub that does work like yours, so i don’t think that is it. 
Can you not make a preset of your preferred settings in that Nvidia Software so your systems knows what settings to go back to or manually start that with 1 click ?