Mine is a G928-F.
I logged a call with Samsung who advised me by email to do a factory reset (full text below). I was sceptical this would fix it but sometimes you have to try these things if you want to progress it further. It didn't fix it for me...mayble I am just too cynical having worked in IT for nearly 40 years!
I would recommend you perform a full factory data reset on your phone. A factory reset will erase all of the information stored on your device and will restore the software to original manufacturer settings. It will not remove software updates but it can undo any changes to settings that might be causing you problems.
In order to back up your data, you will need to install Smart Switch onto your PC. You can download Smart Switch from the following link:
Transfer Data from Samsung to Samsung Galaxy | Smart Switch
Once Smart Switch is installed, please follow these steps:
1. Connect your device to your computer using the Samsung USB Cable that came with your device (the charging cable with the plug head removed)
2. Open Smart Switch and click the Back Up/Restore tab.
3. Click Data Backup
4. Mark the check box next to the content you want to back up. You can select all content by marking the check box next to Select all Items. Click Backup.
5. Click Complete when the backup is finished.
6. You can have Smart Switch automatically back up your device every time it’s connected by clicking the check box next to Automatically back up when USB connection is established.
To factory reset the device please follow the next steps:
1. From the Home Screen, tap the Applications menu item.
2. Tap on Settings.
3. Scroll down to Back up and Reset.
4. Tap the Factory Data Reset menu item.
5. Tap the Reset phone button.
6. Tap the Erase Everything button.
If you rquire additional assistance, please contact us on 0330 726 7864 (UK) or 0818 717 100 (EIRE)z