Cannot Reliably Connect Devices Home Internet

My guess is that this is related to congestion and the T-Mobile gateway switching the tower and band the device is connected to when trying to determine the best connection currently available for what you are trying to do.  Although T-Mobile's internet can multitask basic things.  Mobile internet is no where near at the level of being a replacement for Fiber connections or a good cable connection.  Those larger streams of bandwidth that would allow you to game while streaming and uploading content all at the same time while still doing other things through connections like what fiber and cable offer just aren't possible over cell towers.  Especially in areas with congestion issues already.

You should reach out to support though to get the most accurate answer possible.