Replacement Gateway same as old one

Currently T-Mobile has three different 5G home internet gateways. The Nokia, Arcadyan, & the Sagemcom Fast 5688W gateway. The official word is these are intended to be pretty much equivalente in that one is no intended to be different in any significant way. The most recent Sagemcon gateway was added to fulfill the demand for additional inventory for subscribers. The Sagemcon is very equivalent to the Arcadyan gateway. 

Both the Arcadyan & Sagemcon require management be performed via the mobile application. Both have a very limited WEB GUI reporting capability. The Sagemcon is more spartan than the Arcadyan. Obtaining more information about the operation of either of these is only possible via the mobile application. The mobile application can only access the gateway from the local WIFI. (normal operation) The prior Nokia can be managed via the WEB GUI and the mobile application and provide much better reporting and a superior experience for management via the WEB GUI interface. (my opinion)

Regarding disconnections to the cellular source. With any of the gateways this is the one common beast to deal with. I know some T-Mobile support techs will state upgrade issues with the tower and there is some truth to this but it is NOT universal. The common signatures I observed with equipment upgrades in our area was the repeated disruptions during the middle of any given business day. The behavior might go on for a week or only a few days. With the Nokia it is much simpler to use the browser and check to see if the PCI values for the 4G LTE and 5G NR cellular signals flip and change when disruptions take place. The mobile application can also report cellular metric information I just find its use unpredictable and more effort. When you are trying to solve a problem being stuck doing so on a small screen navigating a menu is just not a positive user experience. 

Re: Diagnostics

You can leverage the management "tools" at your disposal to get as much information out of either the browser or the mobile application. Using the cellular metric reporting does help explain behavior. The PCI or physical cell identifier will tell you if the signal you had prior to a disruption is the same one as you have after a disruption. The other key bit of information is the cellular signal. Does the 4G go from B2 to B66 for instance and also does the 5G go from n41 to n71. If you see the frequency change from before and after, the gateway is not staying connected to the same cellular source. In some cases this could be due to equipment maintenance but this could also be due to the gateway location being between two sources and the signal receive strength drops and a move to the stronger signal source takes place. Factors can change and like a cell phone moves from one tower source to another the gateway might also move to a stronger signal source. In a busy urban area where tower maintenance is taking place this can be a reality. Once the maintenance is completed then things tend to settle down. The LED bars on the display are rather generic and no provide proper diagnostics. You can see if the signal is weak or strong but nothing more useful there. Only with the cellular metrics from the management application can you see more and have a bit more of a clue as to why a disconnect has taken place. 

With the information below it helps to know what is going on:

PCI physical cell identifier

RSRP radio signal receive power

RSRQ radio source receive quality

SNR/SINR signal to noise ratio

The PCI associated with the 4G LTE and 5G NR frequencies helps to be able to locate a cell tower. One of the best tools for that is CellMapper.net. It takes a little exploration to learn but is not too hard. Their database is roughly 80% complete so not all cellular sources are recorded. Knowing where the tower is in relation to your gateway is helpful especially for improved placement and expectations. If you are a long distance from a tower expect slower speeds and possible unpredictable behavior. External influences are always a factor to consider with cellular. Trees, buildings, rain, other RF sources etc… all have to be considered. If you are in line of sight of "the" tower with the cell and nothing is between the gateway and the cell a solid clean signal is quite possible but in many cases a clean direct line of sight to the cell source is not the case. Too much inteference and the signal can be marginal or not work well at all. Good cell coverage for every location is often difficult or in some cases not possible without a much larger investment. 

If the service was working for a long time and becomes flakey well, it could well be due to an upgrade that has changed the equation. Some of the gateways are prone to heat issues and need a fan to help cool them. Some have SIM trays that don't work quite as well as they should so SIM connections can be another factor to consider. Are the contacts on the SIM card clean? Is the SIM properly seated in the tray making proper connections on all the contacts? Sometimes a simple SIM card reinsertion can help. Be sure to power off the gateway before doing a SIM card reinsertion. Be sure when posting to the community conversations to include specific information. Gateway model, cellular metrics, gateway behavior etc… The more you share on the community the better the responses you get. Don't rule out Reddit and the T-Mobile subreddit forum or Nater Tater's YouTube videos. Those are good sources of information. There are others as well including the T-Mobile FAQs for some things. 

Speaking of How Tos: https://www.t-mobile.com/support/phones-tablets-devices

**Page down to the lower part of the page and expand the “T-Mobile Home Internet” menu option.

Well, I hope something here is helpful. I know others could add more to the discourse. Got to go.

Best of luck, hope you get your internet nirvana!