T-Mobile Internet and Storage Server Issues

I am not experiencing your problem, but I do have a pretty robust network connected to my KVD21 gateway via Ethernet. Are you using a router as well, or just the gateway? Are you connected via WiFi or wired interface to your server?

Maybe there is some protocol that the storage server is running that is causing the problem? I use an iMac as a storage device as well as a Plex server, all connected via Ethernet through a Netgear Gigabite switch at the iMac side to another Netgear Gigabite switch where the gateway is located and then into the back of the Arcadyan KVD21 5G gateway. I have no problems, but if I'm streaming and scrubbing a video, I will notice some latency compared to my old setup with Xfinity.

Is there any chance you can temporarily connect the storage server directly to the gateway via Ethernet to see if the latency disappears?

As for the inconsistency of your Internet signal, we all have that behavior. As I understand it, the towers give priority to voice communications when there is a bandwidth crunch, and then return everything to normal once the tower's traffic lightens up a bit. As I write this, I have 68 Mbps down, but during the day it can drop as low as 30-35 Mbps, depending on how many people are connected to my tower.

That's why T-Mobile doesn't sell Internet access the same way, say, Xfinity does. The speed is designed to fluctuate, and the more robust signal you get, the better the overall performance will be at your location.

I hope some of this rambling helps your situation. ¡Buena suerte!