Did you change the standard ringtone?
It needn’t be deleted.
If you still got the ringtones, but with numbers instead of names, yours might still be there.
But since it’s got a number now, the name is no longer to be found and the phone returned to the standard tone.
Hello and welcome to this forum, even though it’s because you are having troubles.
It definitely ain’t normal and seems to be something different or more severe than what @hypnotoad posted, if all the directories are empty.
That’s something for the tech-addicts here in this forum, as it is clearly beyond me.
Have you done anything else, besides updating the phone?
All available information could be helpful for locating the problem.