No/bad signal after marshmallow update

Try resetting network settings.  This will require signing into wifi again.

if that doesn't help....

If you have a Best Buy near you, have the experience desk diagnose.  You can also try new SIM cards.   

Same here.  This is complete bull crap.  

Extortion, is it what it is.  And you've been doing it for quite sometime.  


Galaxy S6 Edge+

Have you tried wiping the system cache?

1. Turn off your Galaxy S6.
2. Press and hold Power, Volume Up and the Home button.
3. You'll see a blue screen with the Android on it, then you'll be taken to the recovery menu.
4. Use the volume buttons to scroll and highlight Wipe Cache Partition.
5. .................

see more here 

Wiping the cache is a joke..

When the update first hit (I have an S6 active), EVERYTHING was dead and phone kept restarting... only fix was up login to google play and update every app. That helped with the restarts but the cell signal still drops.  It was a lot better than before but a subsequent OTA update make it spottier again.

ATT makes us wait MONTHs for an update the world saw in the spring... only to have it be garbage. Not sure why we put up with it.

I've also noticed my bluetooth connections also drop periodically without touching the phone