Arcadyan KVD21 Will not connect to internet on Band N41. N71 works fine

It sounds like you need to get in touch with a customer retention specialist at T-Mobile. Obviously you are getting no place just calling into support. I once managed to be passed up to a customer retention specialist and got the answers I needed. If nothing more than getting connected to an elevation engineer that can investigate the behavior properly and provide answers that would be some progress. 

Maybe there are so many people out there just clamoring to get T-Mobile 5G home internet that they don’t care but they should. Hopefully you can get to the right person that will provide answers and help. 

The way T-Mobile leverages the HetNet it becomes a balancing act to position the gateway so the LTE is able to do what it is intended to accomplish with the split signal radio bearers. From conversations in the community it seems to me users on the n41 frequency on the secondary channel are more challenged in higher density urban areas where user loading on the cells is higher. I personally believe this is due to bandwidth throttling and also the bandwidth is shared with phones which have higher priority due to the nature of the cellular usage. 

If you are interested in understanding the HetNet better:

https://prateek-mishra.medium.com/en-dc-overview-62d35521edc4

This is an interesting and informative overview of how the use of the 4G LTE and 5G NR frequencies are used to deliver service. It is the best explanation I have come across and it does not take a masters in radio technology to grasp the concepts.