This is a non-technical Lounge. We don't work for Adobe.
I think you'll need to contact support again and give them your case number.
Because that worked so well.
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This is a known bug that Adobe has acknowledged in the official Adobe feedback forum: Lightroom 2015.7/8: Panels and filmstrip black when switching to Develop macOS Sierra | Photoshop Family Customer Commun… The only known workaround is to roll back to a previous version (see the bug report). Frankly, I wouldn't waste more time with phone support.
The third guy on support told me about the known bug and I rolled back to the previous version. Still pretty terrible that the first two didn't know and led me down the wrong path. I'm a photographer, I'm not on these forums. Adobe should have informed users proactively. Pretty bad there are probably so many others out there struggling with this problem and (from my experience) 2 out of 3 Adobe support people don't know enough to give them the right answers. Known bugs should be handled better than having a persistent user have to call three times and spend hours of his day trying to get it resolved. Whether this is the right forum or not (which was my best guess as a casual user picking this one) still pretty terrible service.