I think your device might have detected corruption in its internal memory/SD card and trying to correct them to prevent damage to the OS. try removing the SD card and see if this issue persist, if it does, then the internal memory is the culprit.
you wanna try these if you have advanced computer knowledge:
(phone must be rooted)
https://forum.xda-developers.com/showthread.php?t=2165870
keep back up copies of your files.