It seems to be just a bad design.  I believe there needs to be a sheet of aluminum or copper inserted between the hashing boards.  You can see the center area between the hashing boards heats up and the top and bottom heat sinks do not heat as much.  I am very sad.  I wish I would have just got an S9.

I got an R4 of the latest batch on Jan 13, 2017.  It ran for 3 days and one board quit hashing.  I am noticing there is a flaw in the cooling algorithm. Sometimes after a reboot it runs with both boards at 80 degrees and the fan fluctuates periodically.  Other times the fan runs slow and one board runs at 100.  There is definitely something wrong with the fan controller in my unit.  My basement room is humidity controlled and never gets above 68F.  I am so bummed out because I was so excited and spent $1200 to get it.  I also read the website many times and some pages tell you to ship back the board and other pages tell you after Sept 2016 to return the entire unit. I am waiting to see if I can ship the board since I already removed it.  It is pretty obvious by reading the kernel log which board is not hashing.  My guess is they know the defective boards exit and they want you to ship the entire unit in hopes that will make people reluctant and will just run the 50% hash rate and save them some repairs.  I plan to play like a good player but if they don't fix my board I am going to be quite vocal about it. After reading this forum they are not QC these boards very well so buyer beware.