Hi again,
very complex topic, I’m afraid. This boils down to the PC configuration and components used.
Different RAM modules could behave differently, the chipset used also make a difference and the same chipset from different MoBo manufacturers could behave differently, the CPU model also plays a role, of course. I recently had a very lengthy (and useful) discussion with a DAW builder on related topics…and… just, wow 
I’m no specialist here, a system builder with experience with many different components or a tech with experience with overclocking and real-time applications could help better.
Frankly speaking, I always buy components which match perfectly, all up to the maximum supported stock speed just to avoid messing with this stuff.
The problem is the internal multiplier, which can do odd things, another example: I have a PC (not a DAW) with a CPU supporting max 1600, with native 1600 modules. For some strange reason, the BIOS clocked the RAM to 1333. I experienced odd crashes and started trouble-shooting the installation, to no avail. Until I found the mismatch in the BIOS, set the memory to it’s 1600 native speed - never had a single crash or instability since then (6-8 months ago?)
I mention this because if you have a CPU / RAM mismatch, it might be possible to find a ‘sweet spot’ that makes all work fine - the RAM speed is determined this way: RAM Speed = Base Clock Rate (BCLK) * Memory Multiplier, so playing around with those values could help. People useually buy faster RAM when wanting to OC.
But let me add, boldly 
that this should be done by people with experience in this field - I would not do that myself.