I'm curious why is it so?
Rig 1 (6 cards, 3 Gigabyte, 3 Asus)
80% tdp, +180gpu, - 500mem
STABLE for weeks (never crashed)
Rig 2 (7 cards, all Asus Phoenix)
76 TDP, +150gpu, -500mem
FREEZES every few days
Rig 2 still freezes while rig one has never had any issues.
The only difference is the motherboard, which again is the exact same manufacturer and it's just Z170 vs Z270 (MSI Z170/Z370 Gaming Pro Carbon).
Rig 2 also has a beefier and much better quality PSU (Seasonic Prime Platinum 1200W vs Corsair RMx 850W on Rig 1).
Is there anything I can do?
I'm mining Neoscrypt.
Your GPU cards are also different from rig 1 and 2, that's explains it, usually they have different types of mem clocks sweet spots, just play along with it, until you discover its stability for underclocking or overclocking.
sometimes, a riser is also at fault, ensure those risers are reliable.