since MN is out, all my miners are getting 70~80% shares rejected on this chain, no matter what pool i point at.
miners hashing with claymore dual 11.8
when hashing other coins with same SHA3-keccak algorithm like MAX or Smart-Cash is just fine
dev, something is wrong for sure
Are you sure? If a pool has unreworked stratum - as Suprnova or some lesser yaamp pools has - all problems with rejects and double shares can be solved by adding -m 2 param (difficulty multiplier).
On BSOD pool you dont need that param completely because they have updated stratum to avoid rejects on keccak.