Slow speeds on x750 with EP06-A

I’m having issues with a number of X750s deployed in the US (T-mobile). Some work just fine, but others, despite similar signal conditions, have little to no data throughput. I’ve tried switching bands, but that doesn’t seem to help. Here’s an example of what I’m seeing

Devices performing normally…

New Jersey
QCAINFO: "pss",2250,100,"LTE BAND 4",1,397,-93,-13,-59,12
QCAINFO: "sss",5035,25,"LTE BAND 12",1,38,-72,-8,-54,0
CSQ:27 RSSI:-59 dBm RSRQ: -12 RSRP: -94 SINR: 12
30 ms (google pings)
10.16 Mbps (5MB download speed test)

QNWINFO: "FDD LTE","310260","LTE BAND 2",650 (no aggregation)
CSQ:18 RSSI:-78 dBm RSRQ: -10 RSRP: -106 SINR: 15
70 ms (google pings)
7.08 Mbps (5MB download speed test)

QNWINFO: “FDD LTE”,“310260”,“LTE BAND 4”,2225 (no aggregation)
CSQ:27 RSSI:-72 dBm RSRQ: -8 RSRP: -100 SINR: 13
44 ms (google pings)
5.63 Mbps (5 MB download speed test)

Device performing poorly…

QNWINFO: "FDD LTE","310260","LTE BAND 4",2250 (no aggregation)
CSQ:27 RSSI:-59 dBm RSRQ: -13 RSRP: -94 SINR: 10
38 ms (google pings)
0.31 Mbps (5 MB download speed test)

I’m at a loss for why this could be. Signal looks comparable to what the other devices are getting. I’ve checked with the carrier, the line has no restrictions, no network issues reported locally. All these X750s are running the same firmware and configurations. And yet, a number of them (Nevada, Arizona, North Carolina) are experiencing unusable data speeds. Looking for ideas on what else to test to determine the root cause. Any ideas?

Oh, I should also say that the sites with poor performance also have MT300N-V2s with Huawei USB modems sitting right next to them. These devices have no problem producing speeds of about 7Mbps and they are dual band (B2 / B4) with no carrier aggregation.

You can read this post. SPITZ GL-X750 carrier aggregation not working