Thank you for this information. We will look into what is happening with v5.0.8. It must be some other problem with it now.
Do you notice the disappearance while using iReal Pro, or is it when you come back to it from another app?
Do all the playlists disappear (how many did you have?) or is it just a few (the same ones each time?)
At the time they disappear, is iReal Pro running in the background or not, do you know?
Does it happen after you do some specific things in iReal Pro?

If you have any other information, please let us know.
Thanks for your help.