Need a sanity check on an AT&T ASE(Metro-E) circuit.

I'm not really sure of all of the terminology, but we have AT&T's ASE to connect 6 of our locations together. One of the locations is our main one, and the other 5 just need to be able to communicate with it. The main location and one of the other locations had a bandwidth of 100mpbs, while all the others had 8mbps.

Now, we needed to upgrade the bandwidth at the non-main location from 100mbps to 600mpbs, and so we did the same at the main location. However, I am only pushing around 48mbps(I tested using ntttcp and a normal SMB file transfer), which seems like something might be capping things at 50mbps.

None of these locations are pushing any real traffic most of the time so it's not congestion, I checked. Also, I'm not really sure we got over 50mbps before the upgrade either. I never really tested it other than running a quick Internet speed test a few years ago when we upgraded that non-main location from 10mbps to 100mbps. Back then, I got a speed of around 50mbps and assumed everything was good since our ISP was 50bmps. The reason I mention this is because back when this connection was set to 10mbps, our main location was set to 50mbps. I'm wondering if something just didn't get changed at the main location.

So I put in a ticket with AT&T, and they ran some tests and they are saying that they are getting 500mbps+ between the 2 locations between their equipment (Ciena boxes. I don't know the model number, but they are fairly new).

I have checked everything on our end, and there is nothing that would be limited things to 50mbps. It's all negotiating to gigabit all the way to the ASE's Ciena boxes on both ends.

Does anyone here have experience with these circuits? Assuming ATT is right and their side is OK, is it possible that this limitation is on the Ciena port facing our network? That's really the only thing that I don't have access to AND that ATT might not have checked(They checked between the Ciena boxes. I'm going to call them this morning, but I just wanted some opinions to see if I'm even on the right path.

Thanks in advance for any help you can give me.