You are overstressing the Stop and the Blix. You probably have retained silver. You may have overdeveloped by the carryover of developer. After all, 6 16x20s is 4x6 = 24 8x10s and IIRC, they suggest not more than 25 8x10s in 4L (without replenishment) or have I got it wrong? That is way on the high side for all solutions. They are not bad, they are exhausted.