Apologies for some delays in my response, the family's a little sick, and I've been a little sick myself as a result. I'm mostly fine, but not fully 100% yet.
Have you tried disabling RDMA and enabling Jumbo on one of the machines? Because a few things have changed in a short period (network card and a few settings), I'm trying to pinpoint this to a specific element so we can hopefully find a better solution.