It can be really frustrating if the game isn't loading. You mentioned that it's not loading after the update - do you mean the most recent update from earlier this month in August that brought the Android Google Play version to 12785? And you were able to play on it before August's update I'm assuming since you had many many hours on characters and worlds.
The save icon down on the bottom right is displayed as a small eye that goes around in a circle, not as a "green ring" (Thorn Chakram) anymore, so I'm wondering if you're not updated to the latest version yet.
Regarding your backup that you're not able to access - was that done by copying a local save to a cloud save in the Terraria app? Did 505 Games give you a reason why you're not able to retrieve that cloud character anymore when you opened a support ticket with them?
Be sure to give 505 Games as much info and details as you can in the support ticket you have with them about the circumstances that occurred right before you weren't able to play anymore. The more details the better as you might be able to really help them pinpoint and issue and find a solution for your problem and others if others are experiencing the same scenario.
And also, be sure to let the game save completely before exiting the menu screen. Let the swirling little red eye (save icon) completely finish as that may be contributing to some of this. I can't say for certain if that's what's happening, but based on the pattern of your Note 3 working fine and then not working, as well as the same situation with the LG G4 working fine and then suddenly not working, it might be something to watch.
I'm hoping that even if 505 Games isn't able to completely get your game back on track (and that would be a huge bummer, sorry to hear that!) that you might be able to give them some info so that they might be able to find a solution for the future.