I'm trying out Alpha 10 ! Awesome update, lot's of new stuff to try out........this is impressive. And, I tried out my block problem. It's better, the hv design with this white/disappearing block problem still spawned in with this problem but I can fix this now by replacing the blocks. I'm almost certain now that this problem is centered around a design that uses too many of the 6 way cylinder blocks. If I reduce them, split them up with other block designs rather than an entire inner hull ( 2nd layer ) made of only the 6 way cylinder blocks then this problem does not occur.
What is the triangle count of the structure ? it's possible you went over a limit which could be to do with unity's 65k triangle per chunk limit
