Your device requires enough storage to run properly. Then you may want to delete some apps or photos etc to make storage space available. First, check your storage to find out what’s taking up the most space on your iPhone or iPad. Low storage or no available storage is can be a cause of the iPhone or iPad restarting. Your iPhone or iPad requires enough storage.
On your iPhone or iPad, update your apps.
Some viruses are designed to reboot or crash your computer. Therefore it is really important to fix this problem now to prevent future occurrences. It may cause you to lose data or miss important phone calls. When your iPhone restarts unexpectedly, it may create inconvenient even disastrous results. Due to any number of reasons, such as battery problems, software issues, bad apps, you may experience this problem.