Can't boot into custom recovery on Cyanogenmod 12.1
Since your device is an AT&amp;T device the proper way to install TWRP is using loki script and binaries follow those steps to re-install TWRP.


Go to this page and download the latest flash-able zip choose => twrp-2.8.6.0-d800.zip
unzip it on your computer and then copy the recovery.img inside the tmp/loki directory and replace the loki.sh with this script.
open a cmd or terminal and type the following commands .



    adb push /path/to/tmp /data/local/tmp
    adb shell
    su
    cd /data/local/tmp
    chmod 777 loki.sh
    chmod 777 loki/loki_flash
    chmod 777 loki/loki_patch
    ./loki.sh
    reboot recovery
 


the phone will reboot into recovery 


** note you can also copy the tmp folder we created using a file explorer on your phone and execute the last seven commands in the terminal emulator on you phone too.