Same issue. To resolve it, we had to activate developer options. you do this by going to settings, about phone, software information, then click on build number around 5 times (a pop up will show how many more times you need to click it).
Go back into the main setting list and click on developer options. Scroll down until you see "Mobile data always active", click that on.
This corrected our issue of not receiving notifications and uses little to no lte/5g data.
Hope this helps!