Missing menu 'About>Software Updates' on Stock HTC One M8 Android 5.0.1

Question

In the 'Settings > About' there is no 'Software Updates' on my phone. I'm also expecting to receive Android 5.1 OTA update, and nothing comes. Why is there no 'Software Updates' menu on my phone (what did I do to end up here?) and how do I bring it back?

I know now that if I restore both system and data (and boot) then the update menu is there, and I receive an OTA. If I don't restore the data partition (only system+boot) then the update menu is not there and there is no OTA. It is not normal, but how can I modify my Data partition to make the software updates available again?

Device

• HTC One M8
• 5.0.1 Stock System - but I have once modified a file on system partition, and then restored original System+Boot, but not restored original Data partition from before time of modifying system.
• TWRP recovery

History - What did I do?

I installed stock android on S-ON unlocked phone and OTA'ed to 5.0.1. I then installed TWRP, made backup of all partitions. This is the backup I can now go back to. I then rooted phone, installed my apps with titanium backup, and also applied an sdcard fix editing /etc/permissions. The sdcard fix didn't work, but it was an edit of /system, so might be relevant. I didn't notice when the update menu disappeared. On another phone, HTC One m7, I did the same - except the sdcard fix, and the update menu is still there

When I now revert to stock /system, the update menu+OTA does not reappear, but if I restore /data as well I see the update menu+OTA. If I then root phone and apply sdcard fix the update menu and OTA are still there. Though I suspect that the update-menu might vanish sometime in the future after modifying system, and its just a question of it not having realised that /system is modified (pure speculation).

Note on TWRP recovery

I know I wont be able to install the OTA while on TWRP but the OTA should be available, so I see no point reverting to stock recovery before its working again.

Answer 1

Because you have written to the /system partition, it has locked due to the way how updates are installed, they just patch files ie. NO full system image and thus, to prevent bootloops, bricking, malfunction etc., they simply remove the OTA option.

Also: This state is saved and never checked again (because if you have tinkered /system it is intentionally permanent. Restoring /data removes this information and allows a check by the system.

It's similar to how Samsung phones detect if they have been modified; it's not instantly after the installation/reboot, but rather after a few checks (file existence, permissions, sizes, dates, hashsums etc.). This may or may not require some time to finish.

Last note: The availability/existence and extent of those checks may vary depending on the ROM's revision, the model and additional modifications by carriers or the manufacturer itself.