Interoperability of z390 & 4x32GB ECC Udimm's

Hi AsARocks!
I'm stuck with interoperability puzzle about trivial (at fisrt glance) config:

1) ASRock Z390 Phantom Gaming 4
2) Intel 9600k
3) 4 x Samsung M391A4G43AB1-CVF (ECC Unbuffered DIMM, 32GB)

Config works like a charm in cases:
1) 1 DIMM in SLOT B2
2) 2 DIMMs in SLOT B2,A2

all DIMMs where tested in B2 succesfully, but:

Config don't work at all in cases:
1) 2 DIMMs in SLOT B1, B2
2) 2 DIMMs in SLOT A1, A2
3) 4 DIMMs

Thanks in advance for any advises about trobleshoting in such cases.

WBR,

Vitaly