How to uninstall a system app using adb uninstall command (NOT remove via rm or any other way)

Have to mention this to avoid possible confusion, this question is *not* duplicate. This question is specific to **using adb to uninstall a package**. There are several similar questions but are all different from this one, as they're focused on removing an application by any means. *Please do not provide answers using "rm" command to delete the package files. Also, answers related to malformed package names, or trailing carriage returns. I think they're pretty much all covered in all the other questions.* I had pm uninstall functionality but after ROM upgrade. Some things won't uninstall anymore. For example the following two system apps (which I removed under previous ROM, significantly improving overall performance):
/system/priv-app/SecurityCenter/SecurityCenter.apk=com.miui.securitycenter
/system/app/Updater/Updater.apk=com.android.updater Now I get an error trying to pm uninstall them: **Failure [DELETE_FAILED_INTERNAL_ERROR]** But other **system** apps (which won't uninstall through regular android interface) do uninstall via pm uninstall command. Example:
/system/priv-app/Browser/Browser.apk=com.android.browser So both are system apps, what could be the difference between them? For reference, I upgraded from MIUI 8.1.6.0 to 8.5.3.0, and re-installed TWRP and SuperSU. This question is not specific to my ROM, as I see other people are in the same situation. But I seem to have an advantage being able to be able to uninstall some system apps. And am willing to contribute, to find a solution for everyone, to uninstall any app. I tried: mount -o rw,remount /system but that didn't solve it. Please help out with any ideas along the way. Thanks! --- *Update 1* - Confirming steps to avoid intermittent issues
* Wiped all partitions in TWRP
* Installed Latest ROM (MIUI 8.5.3.0)
* Went back to TWRP, wiped only /Data
* Restored /Data from backed up version of the ROM that came with device (MIUI 8.1.6.0)
* Now after I boot into OS, ROM shows as latest (MIUI 8.5.3.0) in settings Now I am able to pm uninstall every app I've tried. Even the most resilient: Google APP, Updater, Security. This Frankenstein.. err I mean hybrid ROM works fine so far, and I've already removed many system packages, making the phone (Redmi 3S+) visibly faster. But I would still like to pinpoint what was causing this to make it into _Generic Solution_. So, if it ain't broke I'm willing break it, so next time it breaks we will know what's causing it and how to fix it. *Update 2* -
* Wiped all partitions and restored all partitions from Original ROM.
* Restored to factory settings (using TWRP)
* and after booting into ROM, went back to TWRP and made another backup
* Using same scenario as in Update 1 above, with only exception of using /Data from here. pm uninstall does *not* work. Any thoughts on the differences between the two /Data partitions I should be focusing on?