Iphone hotspot not connecting

I signed up for unlimited data and a personal hotspot with T- mobile for my Iphone11, for a second home that has no internet.  I would use it only about 8 days a month to stream TV on a single device. 

So far it has connected 1 of 10 times after multiple trials.  My son has Verizon hotspot and an Android phone and can connect instantly every single time, exact same location.  

Why won’t it connect?