LAB testing confirms this issue is not fix for MX uplinks.
Resolved a bug that caused some 48 port MS150 switches connected to MX gateways to experience reductions in uplink throughput if the uplink was connected to any port in the 41-48 range
If your MX uplinks are in a MS150 MGig port move them to a standard ethernet port. You're customers will thank you!
Also don't use MS18.1.4 if you have SFP's in the switch. They will start to flap. TAC case for that is back to development and they are talking mid January.