I left my phone(samsung galaxy j3(2016)) on table before going to sleep last night. This morning when i booted it up, everything went back to default. I just assumed somehow my phone did a factory reset, but i noticed the old wallpaper and some apps i've installed in the past are still there(reddit, assistive touch, facebook lite,..). I had about 5 apps transfered to sdcard(clean master, duolingo,...)and a music player(samsung music)which i think was default app on my phone(since there was never an option to unistall it), and all of them are missing, but seeing the available space i have left look exactly like when i had all those installed. Everything else seem normal, my files on both device and sdcard are still there. Also, i have some disabled apps from back then(i never re-enabled them though), but they were enabled this morning. So i wanna know if my phone was factory reseted automatically or something happened and it only affects certain apps and if possible, a way to return it to normal.
A phone should never do a reset on its own. And while you may have set it to not auto update, it is still possible the OS itself would update on its own. Additionally, while you can set all your apps to not auto update, google will still update things. I have even run into legit apps that in turn install things on the device.
If the space is taken up then something is still there. You could try starting the device in "Safe Mode" and see if the data is still there. Note: most apps won't run in that mode. You can also try connecting to a computer via USB cord to see if the files (not apps) are still accessible on the phone. If so you may wish to save all your personal info (files, contacts, etc. just not apps) and do a full "Hard Reset" of the phone to wipe whatever caused the problem.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the phone...
1. Make sure that the phone is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together, until you see the start-up logo on the screen.
4. Once you can see the logo, release the buttons and allow the device to enter the "System Recovery Mode".
5. Next use "Volume Down" button to get to the "wipe data/factory reset" option.
6. When in recovery mode the "Volume Up" and "Volume Down" buttons are how to can navigate and highlight what option you need.
7. Once you have selected the "wipe data/factory reset", press the "Power" button to select that option.
8. On the following screen, repeatedly press the "Volume Down" button until the "Yes - delete all user data" option is what is selected.
9. Then press the "Power" button to hard reset the phone.
10. If you took your SD card out in step 2, when the device is up and running again, reinsert the SD card.
Phones don't reset automatically. However, if you installed something malicious, that could cause problems. Additionally, if the phone had been reset (either partial, which keeps your personal stuff, or full hard reset) there would be different changes. A partial reset keeps your personal stuff, so any files, etc. would still be there. A full hard reset however wipes everything. Nothing would be left on the device or the card other than the original OS and apps that were on the phone to start.
Now if your phone got an update, to the OS itself, that can alter things, or as stated above, if you downloaded something that is problematic it would cause this.
I would suggest checking the phone for viruses and also malware (they aren't the same). Should you find nothing, then you may want to back up any personal files and info (not apps) and then do an actual "Hard Reset" of the phone and start fresh to resolve the problem.
I had my phone update set to manual, so if i never touched update, it will never do so. And i haven't installed anything recently, my phone was working just fine. And by partial reset, does that mean only certain apps are gone? Because there are still some of the old apps there and there is something taking up the spaces that's the same size as my old lost apps.