Tmobile user here, S7. Last few (2-3) days I've had the same issue. Only at home. At first I thought it was just a Cox cable issue, but it has persisted after having rebooted modem and done speed tests. Have not made any changes to phone settings. I called in to tmo and talked to a tech, they mentioned some things to do (use 5ghz instead of 2.4ghz on router, which my router does not support, make sure bluetooth is off, remove recently installed apps, etc). They also mentioned there's a known issue that Samsung is working on? My phone is up to date. I've rebooted, wiped the cache partition, turned off nearby device detect (which uses ultra low power bluetooth even if bluetooth is turned off), etc. No resolution. I have no issues at work (connected via a 7 year old apple airport) but at home the last few days almost nothing is pushing in. I can turn off wifi and get barraged with push notifications. Very odd.
My modem/router at home is a cox provided all in one unit, Netgear N450. I've rebooted that several times as well.
I'll probably be calling tmobile again tomorrow (I have a multi-line business plan with them) and asking for some free high speed data as I'll have to be on the cell network at home until there's some sort of resolution for this.
I feel like I did an OS update in the last couple weeks? And I just did an update check after talking with Tmobile and the OS updated again.