@Gerodie: Please can you confirm the model number and current Android version of your phone, located in Settings > About phone?
It is important to close applications when they are not in use to avoid any potential performance issues which can arise as a result. To do so, please tap the 3 vertical lines in your Navigation bar, and swipe upwards on the preview window of any relevant apps (or select 'Close all'). I also recommend heading to Settings > Device care (or Battery and Device care) > Memory > Clean now.
@Gerodie: If you head to Settings > Device care > Auto optimisation > Auto restart, is 'Restart when needed' toggled on?
If not, I recommend uninstalling any apps that you have introduced to the phone since you first encountered the issue, just in case the problem is stemming from an external source. You can also head to Settings > Device care > App protection > Scan phone, as this will highlight any malware or suspicious activity on the device.
