FWIW, I've ran Pat5 test using PractRand pre0.95 on sfc64 10 times up to 128 TB, and did not observe any failures. I've also used the 0xdf7e5fd0802274af seed from your run, and it also passed up to 128 TB. Test output (and the patch I've used to only run the Pat5 test) is here: https://gist.github.com/flyingmutant/32a30cb09d130e1cd754ca3577f1d8b2