Welcome to the forum. The 3G to 4G step has left 200 owners with a less capable system, but it shouldn't affect the Remote Start or (most) NAV functions.
I have had to subscribe to Sirius to continue the TravelLink service for under $5 per month. I don't need the extra stations.
Make sure that your radio is at the latest & greatest software update by putting your VIN in here:
Check here to see if your Uconnect® system is due for a software update. Simply enter your vehicle identification number (VIN) to check for any updates.
www.driveuconnect.com
When the Remote Start doesn't work, does it show a reason in the information center? Do you get a park lamp flash & horn chirp? Do you have a 2nd key to try?