Here is my own update....
1. I encountered the completely whited out plex, too, among my various "playing around" to see what Brain 8 would/would not do. Not in response to indexing, but during a "let's see what happens when I search for a thought I know exists." Moment of panic. Exited Brain, went back in and all looked fine.
2. Per the request of Matt from Brain support, I sent him a couple of output log files yesterday after errors occurred in Brain 8. Here is his response from just a short while ago today:
"Our engineers have found the cause of the problem, but we have not yet found a solution. We hope to have a new build available soon that will resolve this problem."
Like you, I'm back to Brain 7 for now since I can't get much work done with the software freezing every few minutes. Hopefully "soon" is soon. My husband and I, too, have used Brain since 2009 and I do not recall having had such massive problems in the past with an update.