Hello, I've encountered this random bug before; I just did a clear cache partition and it fixed it for me straight away. I'll post the steps down below on how to perform a clear cache partition:
To clear your phone's cache partition:
1. Connect your phone to a PC.
2. Turn off your phone (it won't enter Recovery Mode if it's on).
3. Press and hold the Volume Up and Bixby/Power keys simultaneously.
4. Once the Android Recovery screen appears, release both buttons.
5. Use the Volume Down button to highlight "Wipe cache partition."
6. Press the Power button to select it.
7. Use Volume Down to highlight "Yes," then press Power to confirm.
8. After the cache is cleared, press the Power button again to reboot your device.
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