It has only been a month since I was last in Boston but this past weekend I went back again and things have marginally improved since September. Thanks to iOS 15 it's now more obvious when I'm connected to n41. I was spotting it in a few more areas than last time. For example, in the South End I never connected to a strong signal of n41 but I did see my phone bouncing between 1-2 bars of n41 and full signal on n71. Speeds on 1 bar of n41 were around 40Mbps in my testing. T-Mobile coverage map is starting to be a bit more accurate I guess.
Separately, most of Boston College's Main Campus is covered by a site on top of 2000 Commonwealth Ave. A month ago I was getting speeds of 20-50Mbps on campus but sometime in the past month T-Mobile fully upgraded the site. Yesterday during the commencement celebration for the class of 2020 I was getting nearly 700Mbps outdoors despite thousands of guests being on campus in addition to the thousands of on campus students and faculty. Even LTE was great at 190Mbps. Inside Conte Forum where the event was held, my phone dropped down to n71 and speeds remained consistently high at around 80-100Mbps.
I also noticed that T-Mobile is upgrading lots of the sites at larger rest areas and truck stops along I-84 and I-90 in Connecticut and Massachusetts with n41. I was seeing speeds of 400Mbps+ at a bunch of them.
I cannot run SCP for any length of time on my S21 anymore. I can start it, put it in the background, and within a minute or two it's just gone. No crash message or anything. I have not taken the step to uninstall and reinstall yet. But I may do that soon to see if that clears anything up.