Hey there 
since Im getting more and more along with this powerful plugin I stumbled on some issues, too.
So here are two things I don’t know why they are the way they are.
Preview fluid container:
Just grayed out and I read two other people here that had the same Issue.
But this didn’t solve my issue. I cant see the fluid simulation at all, only blank grey.
I set all the channels right to see my smoke simulation.
Cache:
Here I found out that using Cache for a longer time right now especially the Interactive way, it works fine, but I stopped it for a moment and try again to turn it on…nothing. No response at all. I push the start button couple of times…still nothing. Switching to CPU…nothing.
The only thing I can do is kill the C4D Task and reopen the project.
So weird…
Some Infos about my workstation:
Ryzen 2700X 16 threads
64 GB DDR 4 RAM
Cache is stored on a SSD
WIN 10 is stored on M2.SSD
GTX 1060 6GB (Maybe that’s the bottleneck here?)
C4D R26 (Updated it today)
Graphic Drive is up 2 date
Any help to solve it would improve my workflow. Thanks
Mischel