[LG V20 Questions & Answers] sentra10550:
I have a VS995 this is how I got my phone to finally take magisk and pass the safetynet check. I'm running software version VS99513A I performed dirty santa to get unlocked bootloader and root access. Now I tried to uninstall supersu threw the app and I got a failed message. I tried going into recovery and flashing the supersu unistaller and that would fail. I tried flash magisk v12.0 and keep getting error message. I got stock in twrp recovery several times and used LGUP and flash either VS99512A KDZ or the VS99513A KDZ. Am not a developer but it seemed as if the boot.img won't take by the magisk zip. Those where my failed attempts for about a week or two. Now on to the success story

Performed Dirty Santa on software version VS99513A. I decide to flash modstock kernaI update v1.1 because it seem to work well with a stock rooted VS995. I flashed busy box in recovery and downloaded the app and also downloaded quick reboot so I could reboot into recovery easier. After reading [MENTION=4955555]poixninja[/MENTION] thread on modstock kernal - stocked with goodies he mention flash a boot.img that was patched with magisk. So I but the phone into fastboot mode and flashed his boot.img onto the phone with cmd (command prompt). I think I might have tried to uninstall supersu threw the app and I think it didn't work after flash the boot.img. So I put the phone into recovery mode the to wipe and then to advance wipe and clear dalvik and cache. After that I went to install and flashed the supersu unistaller and it took. After flashing I wipe the cache that twrp ask after most flashes. I then rebooted into recovery to make sure my twrp was not affected because I had and issue with that in previous supersu unistaller attempts. Rebooted ito twrp recovery then rebooted into system. I think whenever I flashed the verzion logo stayed up longer than normal but the phone fully started up. I clicked on supersu and it said no root access. Turned of the phone and did the steps to get to recovery mode. Once in I first wiped dalvik and cache. Then I flashed magisk unistaller and it went threw with no issue. I wiped dalvik and cache then rebooted into recovery. After getting into recovery I rebooted to system.

Sidenote: I recommend after wiping supersu and flashing magisk unistaller. Once you boot up install magisk apk. I didn't install the apk until after I flashed the magisk v12.0 in recovery. I noticed when I reboot the magisk icon was on the phone but when I clicked it it said go to playstore to download. I had the magisk manager apk on my SD card so I just installed it. The install to longer than normal I think it was because I didn't install it prior to flash the zip in recovery. I didn't get a chance to verify it yet.

Once the phone boot and I installed the magisk app manager I open it up and got green checks for installed magisk v12 and properly rooted. I went to setting and turned on enable busy box, magisk hide, and systemless. But when I clicked safetynet I got cts mismatch. Did some research and read on other XDA magisk thread that it maybe because of custom roms, modified kernals and possible supersu somewhere on the system. The only root accessible apps I had installed during this process was busybox and quick reboot. I did notice the first time I ran quick reboot after getting magisk it did give it root access then it did after I opened it again.

I decide to uninstall quick reboot and busy box. I uninstalled both apps. I rebooted into recovery mode the manual way. First thing I did was wipe dalvik and cache. Then I flashed busy box uninstaller. When the flash was running I say in the command lines that it found supersu. Which I thought was odd so I also flashed supersu unistaller. I rebooted into recovery wipe dalvik and cache and flashed uninstall magisk. Then reboot into recovery. I ran busy box uninstaller one more time to see if it would pick up supersu again and the command lines did not mention it. I flashed back magisk v12.0 rebooted into recovery. Then rebooted into system

Opened magisk went to setting to turn on enable busy box, magisk hide and systemless. Check safetnet and failed I found a magisk XDA thread that talks about common issue. It said I had to check magisk core only mode. Once I did that he requested a reboot which I did. Once back up I first cleared in app manager under show system I cleared all data for google play store, google play service for instant app, google play services. I opened magisk clicked safetynet check and I passed it. I went to search for netflix in play store and it pop up I installed it and it working fine so far. I tried logging into snapchat and I got threw.

Hope this maybe help full to anyone having issues

https://xdaforums.com/v20/development/kernel-modstock-kernel-stock-goodies-t3563887 (boot img and modstock v1.1)

https://xdaforums.com/showpost.php?p=71154562&postcount=4 (Magisk common issues)