I have a site with an MX65 and a MS120-24P behind it. The internet circuit speed is 100M. The connection between the MX and MS is 1GB. When I have a user connected to the switch (with or without a phone in the link) that is only getting ~20MB. If this user connects to the MX the speed is ~95MB.
This is the first time I have run across this (I have 38 other sites). I have an open TAC case to investigate. I am currently being told there is a possible buffer issue and the Dev team is working on it.
Found it. Someone had change the bandwidth on the traffic shaping to 20M. I apparently missed it in my investigation. I fell into the trap of looking for something complicated instead of checking on all the basics first.