This doesn't sound like any component is defective, rather you are using an incompatible combination.
Having multiple sockets on the same memory bus populated increases the capacitance on each data line and slows down the rise time, which can cause transitions to arrive late and be misdetected. This phenomenon is known to electrical engineers as "fan-out".
This is further complicated because of the fan-out internal to a memory module. The number and topology of the DRAM devices on the module, called "rank", will affect how many modules you can successfully connect in parallel.
Server motherboards supporting a lot of memory sockets actually require buffered memory, which uses a cascading network of buffers to limit the fan-out (and therefore capacitance) seen by each one. There's delay caused by the buffers themselves, but it only increases logarithmically with the number of loads, whereas for unbuffered memory capacitance increases linearly.
Wikipedia discusses this: https://en.wikipedia.org/wiki/Memory_rank
Some motherboard manuals actually call this sort of thing out. For others you can deduce the information from the RAM compatibility lists. As an example, the ASUS Z170-A motherboard shows that dual rank (called DS = double sided in the manual) can only be used in two slots at once on that board, as opposed to the ability to use four single rank DIMMs at once.
