I understand that the unit is only working when you have 4 modules installed in the outer blue slots. Could you confirm the DIMM slots you are using? Have you moved the memory around?
I would assume you are installing the memory modules in DIMMs A1, B1, C1, D1, E1, F1, G1, and H1. Let's try to use 3 modules per processor to see if we have the same results (A1, B1, C1, E1, F1 and G1.
I would recommend gathering the logs of your system by using the https://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=24388 Intel System Information Retrieval Utility to review the entries of the boot attempt when we have all of the memory modules installed.
with 4 dimms I have used slot A1, C1, E1, G1.
it is booting with 6 dimms in A1, B1, C1, E1, F1 and G1 as you suggested.
The system is configured to boot when powerd on.
On an unsuccesful attempt with more than 6 dimms the BMC logs only power on /off and nothing in between.
Thank you for the update. This tells that the unit is able to work with more than 4 modules at the time. Now let's see if we can narrow down the issue in D1 or H1. Go ahead and install a memory module in D1 see if it works, and then do the same for H1.
The BMC keeps a historical record of the events of the unit. In this case, you should be able to run the update when you only have 6 modules installed.