I'm impressed by the scale of your cluster, but factmsieve is not designed for jobs this big.
The polynomial is right, and the alim and lp look reasonable, but you're clearly using the wrong sieving binary since you're getting 0.25 relations per Q. I think you should be using 16e, and you should be using three large primes on the rational side (lpbr=32 mfbr=96 rlambda=3.6)
For things this large I tend to start from small Q (eg Q=1e7) rather than Q=Qmax/2.
