[gTen]

1. this one sounds like it may be defective..this is similar to when we underclock phones and when they can't handle the low sleeping voltages it does not turn on..but its a guess hard to say..did this only happen once?

2. you can reconfigure 4g sleep settings in the EPST

3.have you tried temporarily to set it not turn off the screen at all?

4. does this also happen when you get a phone call while phone is on?

5. if this happens multiple times and you can replicate it..try a logcat..

6. you 100% sure that was the 3g icon and not the 1x icon? what is possible is 4g didn't connect and its at 1x and not 3g, thus data would not work.