Semi-Complicated Network

Sorry for the prior long response. With respect to the 5 port switch on Lan2 and the slow down you state. Get into the web-gui of the Nokia and check the stats on the LAN ports. If there are errors or discards that is good to identify. If the switch is managed then look at the statistics in its interface. Don't overlook the statistics of the cellular interface either. The assumption may be that the problem is local or with the Nokia router itself but well maybe not. Check the 4GLTE and 5G signals on the "Overview" tab and make note of the RSRP and SNR values. Compare when the speeds are good vs when they are poor. Also look at the Status tab and compare the primary and secondary signal "Band" for each and confirm also that the PCI for each is the same. Don't assume it is a local issue only. If T-Mobile is working on the equipment on the tower or connection loads on the tower increase that can also impact the performance and speed.