Root and software update - Android Q&A, Help & Troubleshooting

Hi guys, my questions would refer to root privileges with regard to OTA software update...
But firstly...
Do you think that KingoRoot apk constitutes a reliable root service? Do you think one can root his/her device just by installing the app via browser in the phone and launching the root process?
And now the initial question:
Do you think that OTA software update can remove root from the device? Or, does the fact that one can perform OTA software update indicate that there is acutally no root on the phone?
(Device: Samsung Galaxy J5 2016)
Thanks!

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Yannikk said:
Hi guys, my questions would refer to root privileges with regard to OTA software update...
But firstly...
Do you think that KingoRoot apk constitutes a reliable root service? Do you think one can root his/her device just by installing the app via browser in the phone and launching the root process?
Click to expand...
Click to collapse
Generally no - Android functions such as Verified Boot and dm-verity are supposed to prevent persistent rootkits, unless the bootloader is unlocked. Yes, there are some exploits, but usually these only provide temporary root.
As a general rule I advise against using closed source software, simply because you don't know if there's anything malicious going on under the hood. A safe alternative is Magisk, although this does not utilize any exploits, so you would have to unlock your bootloader and root the "right" way.
Yannikk said:
And now the initial question:
Do you think that OTA software update can remove root from the device?
Click to expand...
Click to collapse
Yes - in most cases, a OTA update overwrites several partitions on the device, including /boot and /system. This means that after rebooting from an OTA update, root would no longer be available. The workaround for this is the "Patch to inactive slot" function in Magisk on A/B devices - once the update is complete and the device is ready for a reboot, Magisk uses root privileges to patch the new boot image, so that root persists after reboot.
For A only devices such as Samsung, it's a bit more tricky...you'd need to flash a custom recovery after the update and flash Magisk from there.
Yannikk said:
Or, does the fact that one can perform OTA software update indicate that there is acutally no root on the phone?
Click to expand...
Click to collapse
Not always. In most cases, update_engine conducts various checks to determine whether critical partitons such as /system and /boot are intact and untampered; if they are, the update will fail. This is why Magisk has the "Restore images" function for systemless root - Magisk restores the unpatched boot image written to flash, so that the device may pass these checks. It doesn't always work, and on the opposite end of things, there are some devices that will happily install an OTA update even with modified binaries present on the device.

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Thanks for you answer, V0latyle.
Now, I would present a broader picture of an issue that gains my attention...
It happend some time ago, on an older device (Galaxy J5 2016, as mentioned)...
I installed KingoRoot apk (directly via browser in the phone) and launched rooting process... The app signalized that the rooting process has been successful... I did not install any custom ROMs or apps... The phone functioned pretty normally then... However, after few months, out of the blue, my device started behaving strangely... Videos on YT took a great amount of time to load or they lagged after some time... Newsfeed on IG did not work, nor instastories... Browsers were also considerably slower... Approx. 2 months later, when Nougat 7.1.1 came out and after I downloaded this software update (OTA), the phone got somehow faster - YT videos loaded faster or did not lag, IG newsfeed got updated regularly, browsers were not so slow either... On the other hand, yes, some apps still behaved in an unusual way...
Do you have any idea what might have happened in this case?
Thank you very much for any suggestions!