This may cause by your ram issue. Even with the exact same model and spec for the ram, two different memory kit might be different in batch production line with different part number. Therefor it better to buy Just a pair or quad pair (4x ram in a single package in you want to occupied the ram slot).
AMD treat 3 sticks as a dual bank region and a separate single bank region, but 4 sticks will be a single dual bank region.
Superficially identical sticks that are bought at significantly different times may well have subtle differences in the underlying silicon. Have you tried loosening the timings a little (i.e. keep the clock that seems to work, and increase the timings, e.g. from CL16 to CL18, etc).
Remember that 4 sticks of overclocked RAM is always harder to support than 2 sticks (on dual channel platforms).
You seem to be saying it works ok at 3600? Or is there some problem at that speed?