Hey, here’s a thought…
Why not connect one monitor at a time to make any adjustments.
My intention was to offer a workaround for the side-issue you mentioned, in case it was of use. What you do with it is up to you.
Good luck.
Regarding the main issue, perhaps the black screen is related to the Plymouth splash screen, which is typically a bad player when booting, for many users.
The following article might be of interest; various links to possible solutions and workarounds are also included.
The fact that you are using multiple monitors may indeed complicate diagnosis and potential workarounds. In this case, I also suggest you remove one monitor from the equation while finding a solution.
Cheers.