[General Questions and Answers] ChingghisKhan:
Hi m3tatr0n84,

Sorry to hear about your troubles.

I think the following will get you back to 5.1.1 and root: http://www.droidviews.com/update-att-galaxy-s5-active-to-lollipop-root-it-and-enable-wifi-tethering/

Install Rooted Lollipop ROM on AT&T Galaxy S5 Active

Note:

You can the following instruction of want to update to Lollipop and enjoy root access. Besides, you can install the rooted Lollipop firmware regardless of what firmware or build version your phone currently has.

Preparations

Rooted AT&T Galaxy S5 Active. If you don’t have root access, do as directed below:

Download the following firmware and extract it: G870AUCU1ANE4_Full_Odin.rar

Follow our tutorial to flash the firmware: Link

Then root your Galaxy S5 Active using Towelroot.

Enable USB Debugging on your Galaxy S5 Active. This step has nothing to do with the method given below but it could be a lifesaver if anything goes wrong.

Install Chainfire’s FireFlash app on your AT&T Galaxy S5 Active. Since this new app is only available for beta-testers currently, go to the Google+ page and join the Android-FlashFire community. You must be signed into Google+ using the same Gmail ID that you use on the Google Play Store. Having joined the community, click the Play Store link to download FireFlash.

Download the stock rooted Lollipop firmware for the AT&T Galaxy S5 Active:

G870A_OF3_Stock_Rooted_ROM.zip

G870A_OF2_Stock_Rooted_ROM.zip (older)

Also download the Odin (v3.10.6) OC5 bootloader file: G870A_OC5_Bootloader.tar.md5

Instructions

Copy the G870A_OF3_Stock_Rooted_ROM.zip to your device.

Before you do anything, open SuperSU app on your phone, tap the Settings tab, scroll to Enable su during boot option and enable it.enable-su-during-boot

Open the FlashFire app and “Agree” to the Terms and Conditions prompted by the app.

Press the rounded “+” button twice to bring up the Actions menu.fireflash-app-android

Now tap Flash Zip or OTA option and select the G870A_OF3_Stock_Rooted_ROM.zip.

Make sure that Auto-mount is unchecked under the Options menu and press the check-mark to continue.

From the main menu uncheck all options under EverRoot.

Set the Reboot settings to Download.

When all’s done, tap the Lightning bolt icon followed by OK to begin the installation.

When the installation is finished, your device will reboot automatically into the Download Mode.

Now connect your phone to the PC via USB cable and launch Odin.

Click the PDA/AP button in Odin and select the G870A_OC5_Bootloader.tar.md5 file.

Then hit the Start button to begin the installation.

Your AT&T Galaxy S5 Active will reboot automatically. Just wait patiently for a while. Done!

Enable WiFi Tethering on AT&T Galaxy S5 Active

Note: You must have root access to flash the WiFi Hotspot mod on your phone.

Install FireFlash app by Chainfire (see Method 1 for how to).

Download the Mobile Hotspot mod file and copy the zip to your phone: G870A_OC5_TetherAddOn.zip

Now launch FireFlash and tap the “+” icon twice to bring up the menu and then select Flash Zip or OTA option.

Navigate to G870A_OC5_TetherAddOn.zip file and select it.

Make sure that the Auto-mount option is not selected under Options.

Leave the default settings under EverRoot and Reboot options untouched.

Finally, tap the Lightning bolt icon and then tap OK.

Your phone’ screen will turn black for sometime so do not panic. When it turns up, install the Tether add-on zip file and reboot your device. When your phone boots up, you’ll be able to enjoy free WiFi hotspot on your AT&T Galaxy S5 Active (SM-G870A) running the new OC5 Lollipop firmware.