Galaxy S5 unable to switch to 4GLTE when Wi-fi is turned off I have had my Samsung Galaxy S5 for about a year now and it has been working fine until a few days ago. I would use my wi-fi when I have access to it and then I would switch to my 4GLTE when I don't have access to any wi-fi. This has been working for the longest and I only had to switch to 4GLTE when I'm at working or driving. But recently, my phone would not switch back to 4GLTE when I lose wi-fi connection or even turn off the wi-fi option on my phone. Restarting the phone would temporarily fix the issue but I was wondering if there is anything else that I can do?

I got the phone from T-Mobile but I been using MetroPCS ($60 unlimited data plan) since about 2 months after using T-Mobile.
I suffer from the same issue. I have discovered the following to work for me.

To prevent it occurring: Turning off WiFi Calling seems to work (It's the last item under "Settings >> Call"), if you have it available and on. I've not had to to resort to flight mode (see below) since disabling this.

Countermeasure when it occurs: Putting the phone into Flight mode and back out of Flight mode will restore the ability to connect to 4G, at least until the next time it fails after coming off WiFi.

Hopefully the above will help you avoid rebots.