[Sephiroth]

It all depends on the Post-RS errors and whether or not they are rising. With those SNR levels, it should not be rising much if at all, but the Pre-RS count would be rising significantly; they don't matter if Post-RS is not rising.

It's power level and SNR stability that's required here and an engineer is required as first step if there is no stability. Not that he can do much other than check all the physical bits and your cabinet tap. Then he can escalate to Networks.