Very good signal still buffering

I have the new g4se Gateway for T-Mobile home internet.

Ihave a very good signal and a television that is less than 10 ft away from the Gateway and yet I'm still buffering multiple times a day streaming on multiple apps.

I have tried restarting the Gateway, & I have restarted my Roku multiple times but nothing is working.

I had a different Gateway previous to this one and I did not have the buffering but it wasn't distributing the signal throughout the house so they sent me a different model but it was a complete nightmare of a process and I don't want to have to go through it again. 

I'm attaching cellular metrics and information in the app, does anybody have any idea what could be going on or how I can fix it.