Recore A5 and A6 use 1.35 V on the DDR3 which can lead to instability.

[eliasbakken]

Right now we are using a single device tree binary for all boards. In order to separate those with 1.5 V DDR3 memory from those with 1.35 V DDR3 memory we would have to know the hardware revision.
Alternatively we could increase the voltage slightly so it works better with both versions.
DDR3L: 1.283 > 1.35 < 1.45
DDR3: 1.425 > 1.5 < 1.575
Both should be OK with 1.4 V.