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I'm using a rooted Android 13 device, and an external SD-card that I mount as /data by editing the fstab. The SD-card is partitioned into few EXT4 partitions, and I can boot with any of them mounted as /data just by editing the fstab. For example, my current fstab entry is:

/dev/block/mmcblk0p2 /data ext4 noatime,nosuid,nodev,discard wait,noflush_merge,fsync_mode=nobarrier,reserve_root=134217,resgid=1065,check,formattable,quota,reservedsize=128m,latemount,resize,checkpoint=fs

And I can change it to mmcblk0p3, to boot with a different partition as /data.

But there is an issue. Each time I boot with a different partition as /data, it works, BUT when I return to my previous one (same way, by editing fstab), it's lock screen password/PIN/Pattern no longer matches. It says like Wrong PIN.

Since I don't use encryption, I easily solve it by deleting the locksettings.db file from /data/system. But if I used encryption, it definitely wouldn't work.

My question is why it happens?

Why, when I successfully unlock a phone booted with different /data, and then switch back to previous /data, the password that was set there no longer matches, and I have to delete it?

EDIT: I made an experiment with a clean, not modded phone (without any SD cards or Root), that uses encryption and everything is stock. I took a full backup of the NAND flash, which includes GPT table, all partitions, and therefore the encrypted userdata too. After taking that full backup, I performed a Factory Reset on this phone, and booted up. Then, I turned phone off again, and flashed my full NAND backup. The phone booted successfully, but yes, the password that was set there didnt match.

This result is very weird. What could even get modified on the phone, if not something on the NAND flash?

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