S24 Ultra stuck in lock-screen/reboot loop after OTA to Android 16 / One UI 8 (correct PIN accepted, then boot loop)

[Spockie1701]

Device/Build

• Model: Galaxy S24 Ultra SM-S928B/DS, CZ retail (Titanium Yellow, 12/512).

• Update: OTA from Android 15 / One UI 7 → Android 16 / One UI 8.

• Battery/Charger during update: ~60%, not on charger.

• Not enrolled in any beta programs.

Symptoms (chronological)

1. After the first post-update reboot, entering the correct screen-lock PIN flashes the screen and returns to the lock screen. Entering a wrong PIN shows the expected error.

2. After many quick attempts, the device switched to a black PIN screen, then after many attempts rebooted.

3. A different animated lock-screen wallpaper appeared (not my original one).

4. Each subsequent single PIN entry triggers a reboot, followed by ~10 minutes of the boot animation (“spinning circle”), then back to the lock screen.

5. This loop repeated ~6–7 times. I could not properly unlock the device.

What I tried

• Recovery: Wipe cache partition and Repair apps → no effect.

• SmartThings/Find My Mobile: Remote unlock feature appears to be removed on recent One UI builds, so this wasn’t an option.

• Smart Switch (Emergency Recovery) wasn’t feasible in this state.

• Local Samsung service confirmed that a firmware reflash without data loss isn’t possible; only a wipe/re-install.

Workaround/Resolution

• Factory reset via Recovery solved the loop (FRP with my original Google account after reset). I’m now restoring from cloud backups.

Ask

• Has anyone else hit this exact Android 16 / One UI 8 post-update lock-screen loop on S24 Ultra?

• Any known bug IDs / hotfix builds from Samsung?

• Is there a recommended way to collect logs pre-reset in this state (e.g., adb, download-mode diagnostics) to help Samsung QA?

Repro notes

• Update performed with ~60% battery, not charging; stock device (no root, locked bootloader).

• Issue started immediately after the first post-update reboot.

Environment

• Region: CZ (EU).

• Device: SM-S928B/DS, dual-SIM.

[arianwen27]

Is there any chance this is the same thing as what you're experiencing?

https://eu.community.samsung.com/t5/mobile-apps-services/phone-automatically-relocks-after-one-ui-8-...

[Spockie1701]

Yes, probably the same issue.
In my case the only way to recover any non-cloud data would have been a service reflash.
Our local Samsung service said a reflash without data loss isn’t possible, so I opted for a factory reset, which I as able to do myself (luckily most of my data was backed up).