rooting - Unbricking a FRP-locked phone while leaving it rooted

I have a rooted Samsung Galaxy J1 Ace SM-J111F running the stock ROM in Android 5.1.1. I used this XDA-Developers guide to root it. The reason it's rooted is so I could format the attached SD card as internal storage. I've had no problems for the last 2 to 3 weeks until I switched the phone off in one country and switched it on in another. When the Samsung logo appears, it shows that the custom binary is locked by FRP.

I decided to re-root my phone again using the same method however, the terminal returns:

Waiting for phone to be connected...

Even though the phone is in download mode and all the appropriate settings have been set.

The guide also provides the firmware for the phone, I haven't tried it yet because I fear that the SD card will be have to be reformatted and all my data may be lost. I'm trying to find a way to fix my bricked phone and while keeping it rooted. Unfortunately, there is only one rooted binary available for this phone.

So I ask:

1. Is there any way to unbrick phone and keep it rooted?


2. If I do restore the firmware, will I have to reformat the SD card and will my data be deleted?


3. What caused this issue?

EDIT: I have continued this problem on a different question since it corresponds to a different issue, where factory resetting the phone still leaves it bricked via FRP.

Answer

Unfortunately, there is no way to unbrick a device and leave it rooted (1). You must flash the stock firmware into the device, thereby making it unrooted. Usually this a bricked device occurs when the device has been modified with so much alterations to the point where FRP detects it bricks the phone (3). The best way to counter this is to install a custom recovery image (like TWRP) to safely fix your device.