Tab S8+ acting weird

[Pedro Augusto2]

So 2 days ago i made a deal for a S8 plus tablet. Second hand but as good as new. Not even a scratch. First impressions were great, model and serial numbers matching (SM-X806B). Came home happy.

Then, at 40% batery, i turned on economic mode. SOme time later i noticed a vertical stripe always on the right corner, everytime the screen moved, like a vsync problem. It seens to appear only when refresh rate goes down to 60Hz, instead of 120Hz default.

So i soft reseted and found out that, when shutting down, the tablet show some command line like a Linux distro. When booting up, it shows a debug panel beside the android/samsumg logo, with some of the hardware info. Now i'm also noticing random red flashing on all the edges of the screen, like when it's loading something.

did a factory reset, and some of the samsung aplications would not install, saying it mismatched signature... Can't update android either through the settings menu. Google apps works fine.

Finally, even after the factory reset, the dev's options were already unlocked, with some apps like IOThidenmenu on the app screen.

So, do you guys know why is this happening? Is this hardware /android version a test model? If so, is there a way to rewrite it to a customer mode?
I don't want to keep a expensive time bomb in my hands.

Thank you all

 

[VidJunky]

It sounds like the device has been rooted. That is the only way I know of to have things like developer options still active after a factory reset. I found these directions online for how to boot into recovery, when you do this it will tell you at the top of the device whether or not the device is locked or unlocked which is an indicator that something has been done to the device. https://www.hardreset.info/devices/samsung/samsung-galaxy-tab-s8-ultra/bootloader-mode/

As soon as I searched this a lot of "how to root" directions and videos popped up as well, so I'm going to go out on this limb and say the device has been tampered with.

This isn't necessarily a good or bad thing but there are a lot of ways to mess up a phone through root if you don't know exactly what you're doing, which might explain the glitches you're seeing. It also explains why developer options are remaining unlocked. Did the listing by chance say the device was rooted? You might have an option to return it if it wasn't disclosed that the software was tampered with depending on where and how you purchased it.

The potential for other issues is high too. Being rooted you can selectively pick and choose what is and isn't reset when a factory reset is done. This also means spyware could be added along with other script that could do things like forward communications, keylogger, picture forwarding, you name it. If you boot into recovery and find that yes the tablet has been rooted and you are unable to return it, there are tons of videos and instruction online to guide you through how to see what is one device and how to make your own modifications.

Best wishes, let us know what you find.

 

[B. Diddy]

Welcome to Android Central! I think @mustang7757 could probably walk you through the steps on how to flash it back to the stock ROM.

 

[mustang7757]

Definitely can if OP wants to do that