I have a strange issue with my Samsung Galaxy A8 (2018) phone running on Android 9: The lockscreen keeps recurring automatically roughly every 5 seconds and several system services (keyboard, main buttons "menu/home/back" and dropdown window) are not available. It seems like a problem in the OS firmware.
Here's a summary of the issue: Last evening, I shut off my phone. Everything had worked smoothly until then. Moreover, there had not been any software updates or app installations during the last days. When I switched it on this morning, the following problem existed and I couldn't get rid of it so far:
Unlocking the phone with the PIN after power-on works properly.
Normally, the lockscreen is displayed thereafter and the homescreen can be entered either via fingerprint or via swiping and PIN input.
But my phone shows the following loop periodically:
[lockscreen which does not respond to swiping (~ 1 second) --> blackscreen (~ 5 seconds) --> blackscreen with status bar at the upper edge (~ 1 second)]
This cycle repeats over and over again unless the power key is pressed which puts it to standby mode. In addition, the vibration alarm is repeated similarly all the time when the battery is lower than 15%.
Using the fingerprint sensor, the homescreen can then be accessed. In fact, it shows a black background and not the selected "Galaxy Theme" background". A single app can be started, but everything is interrupted periodically by the lockscreen again:
[lockscreen which does not respond to swiping (~1 second) --> homescreen / app screen without status bar (~ 5 seconds) --> homescreen / app screen with status bar (~ 1 second)].
This cycle repeats over and over again. Additionally, neither keyboard nor the three Android buttons nor the dropdown window nor the task manager work properly.
Therefore, it is not possible to revert to the homescreen and open another app. So only one app may be opened at a time and another app can be used only after the phone is restarted. By the way, the normal way of shutting the phone off does not work, the combination of pressing both power key and volume-down key is required.
However, the basic system functions (e.g. charging / Wifi / Bluetooth / phone calls) are fully functional.
So far, I haven't found an app which has functional deficiencies itself. So the problem must be located within Android.
A few details about my system:
Model number: SM-A530F ("Samsung Galaxy A8 (2018)")