You must downgrade to KitKat & use FlashFire to upgrade back to 0x0 Lollipop with root!
1. Factory reset your phone (stock Lollipop), don't set it up afterwards.
2. Flash official KitKat firmware for your model via Odin.
3. Follow OP instructions to get root.
4. Use FlashFire to upgrade to pre-rooted ROM like this one or this. You can flash the official Lollipop ROM for your device as well and root it during flash, by adding/injecting UPDATE-SuperSU-xxxxx.zip (Flash ZIP or OTA).
5. Flash corresponding Modem & Bootloader via Odin
Don't flash ROMs that come with non-stock kernel and/or recovery - you'll get 0x1.