Congestion at various locations nationwide when crowds are higher than usual.

I wonder if I am the only one experiencing this issue. I mostly use unlocked phones, and my current one is an Axon 7. Frequently when there is a large crowd of people in an area, even with 3-4 bars of signal, I get no service.

I am on the T1 TI plan, and the other phone is also an Axon 7 with the same problem.

Now I am not talking about places with regular crowds, but places where a special occasion caused a larger crowd than usual.

Now the occasion for my comment was at a Premium Outlet mall in Grand Prairie Texas during the Texas tax free weekend, which attracted a larger number of people than usual. But I also experience no service at conferences, concerts or any place at a time when there is a larger than usual crowd.

Now this would be fine and I probably wouldn't bring this up, but I have a FreedomPOP LTE (AT&T) sim card in my second slot of the same phone. I switched my data to that card while I was there, and I showed the same signal bars on my phone, but I had absolutely no issues with that service and the speed was over 15MBPS at the same time. This is actually the reason I keep this card for these occasions where T-Mobile service does not work, and it seems to happen pretty frequently in such situations.

I am just curious if this is a common experience, or whether a phone with carrier agggregation would fair better in a situation like that, or if just T-Mobile does not have the capacity to handle more users than what a place usually has.