[Galaxy Note 4 Q&A, Help & Troubleshooting] LorDElazAR:
If you have checked out, downloaded and flashed RaymanFX's latest CM13 Unofficial Nightly ROM for Note 4 N910C/H/U users here: http://xdaforums.com/note-4/orig-development/rom-cyanogenmod-13-semi-official-builds-t3259878 chances are you failed miserably at getting back to Samsung's Stock Firmware as you have encountered a series of unending bootloops. The bootloops exist because your downgrading from Android 6.0.1 Marshmallow (CM13 ROM) back to Android 5.1.1 Lollipop (Your previous Original Samsung Stock Firmware), however if you've received the Android Marshmallow Update for your Note 4 model number and region as an OTA Update from your device or Manually by downloading it from sammobile.com or any other external link and have flashed it before flashing CM13 no need to worry you won't need a backup of your Samsung firmware (Unless you want one) as you can perform a clean install of your Samsung Marshmallow Firmware via Odin v3.10.7 Here is where the fix lies; i have compiled a series of posts from 2 very helpful XDA Members from the community because from my experience i have managed to rescue my device using their methods which i will mention below.

Firstly if you have made an Efs partition backup from your previous Original Samsung Stock Firmware in the form of a .tar or .img file e.g "efs_backup_2015-06-01_02-37-16.tar" or "efs.img" respectively then you are good to go if not leave this thread.

Also you will need to download a Note 4 N910C/H/U Pit file corresponding to the region of your Samsung Firmware so here is a link to a selection of pit files. You will need to create an account at sammobile or simply sign if you have a current account to see the download links here: http://www.sammobile.com/forum/showthread.php?t=30022

Follow FR34K-B1B0's helpful post on getting back to stock here: http://xdaforums.com/showpost.php?p=65414257&postcount=39 Skip the 1st Step since we are restoring our IMEI using our backed up Efs file and we will be using a different method to restore this backup.AND AFTER ODIN IS DONE FLASHING THE SAMSUNG FIRMWARE there is a chance that your phone will boot to the Stock Recovery and you will notice a message down there saying: "dm verification failed" so simply wipe data/factory reset and wipe cache and then reboot. Afterwards your phone should boot properly. Now close he's post and carry on down here.

After your phone boots up and you have set it you will notice that your mobile is not connected to your specific mobile carrier and you will see the Emergency calls only text on your lockscreen hence the Not registered on network error. Go to Settings--->About device--->Status and scroll down and you will search and find that your IMEI is literally not the one your phone has and that your Serial number is of an Android Serial number given to you from flashing CM13( Since it's a pure stock android software). If you want you can download the Phone INFO App from the Playstore to verify your device's information and if you do so you will notice that your Samsung Serial number is a bunch of 0's like this: 0000000000 or it's not even present hence wiped.

HERE IS THE MOST IMPORTANT PART FOR RECLAIMING YOUR MOBILE NETWORK CONNECTION, your IMEI is wiped and so you must restore it using your Efs backup file which i mentioned previously above. To do so you will need to root your device and the guaranteed way of rooting your device is using Chainfire's CF-Auto-Root Method.

Here are the links to the Odin flashable MD5 files based on your Note 4's Model Number that you must download ---> For SM-N910C: https://download.chainfire.eu/559/CF-Root/CF-Auto-Root/CF-Auto-Root-trelte-treltexx-smn910c.zip For SM-N910H: https://download.chainfire.eu/577/CF-Root/CF-Auto-Root/CF-Auto-Root-tre3g-tre3gxx-smn910h.zip For SM-N910U: https://download.chainfire.eu/557/CF-Root/CF-Auto-Root/CF-Auto-Root-trhplte-trhpltexx-smn910u.zip After downloading the file on to your computer simply load the file through Odin, power off your phone and boot it to download mode then connect your device to your computer and flash the md5 file. After it's done flashing your device will boot to a custom screen with a red android logo then it will boot.

Right now your device is rooted and you will see the Supersu app in your app drawer. Next if your Efs backup is stored on your computer and is of the format .tar simply open it with 7zip or Winrar you will find the .img present then extract it your desktop. In order to restore your IMEI with this .img file we will need an update package that we can flash from a custom recovery(CWM or TWRP). Here is the link to civato's awesome flashable update package: http://xdaforums.com/showthread.php?t=2331853 and you'll find the package down in the attachment. After downloading the attached file, rename your Efs backup file from "efs.img" to "EFS.img" then extract the contents of the downloaded update package to a folder with the same name of the package, copy your EFS.img file to it and use 7zip or Winrar to add the files to an archive(.zip).

Last but not least copy the new repackaged flashable zip to your external or internal sd card. Run Odin and flash your desired Custom Recovery(CWM or TWRP). Boot to the custom recovery and flash the update package and finally reboot system. After booting your phone will have it's Efs partition restored; your IMEI and Samsung Serial number will be back and your mobile network will be back on again. :fingers-crossed:

Special thanks to FR34K-B1B0 for he's helpful post on getting back to stock firmware

And Many Many Thanks to civato for he's really useful Efs restoring update package! :victory:

And last but not least thank you Chainfire for your great CF-Auto-Root Method that helped root our device(s).