Unfortunately it sounds like some oddities that end up happening to a few devices here and there with pretty much any update. It doesn't appear that this is something that has affected most or even a significant number though. That's not to say that it can't happen to someone and that steps to backup data shouldn't be taken just in case when it comes to pretty much any update.
Did a complete reinstallation of my complete backup (which I do always before any update) - BUT again, the music was lost, the U2 album was again reinstalled (though not existing in the backup) and now even MORE pictures were LOST! The resting photos had wrong timestamps (from 2006 to 2018 for a series from 2011 i.e.) and were in fact not accessible by date no more!
THIS is a major bug!
as for the importance of backups:
YES! Never have confidence on apple - not even in the minor update!
In fact, I transferred photos regularly on my MacBookPro, so they are not lost.
I was able to transfer my music from my MacBookPro onto my iPadPro.
As for the photios, it will take a LOT OF TIME to delete ALL photos resting with false timestamps on my iPadPro and retransfer manually (!!) back from my MAcBookPro all the about 2000 photos I need on my iPadPro!
This will take me roundabout 50-80 hours at least.
And: NO! This is NOT a good job done by apple. As I found out today, I am not the only one concerned by this big bug.
Maybe, this converses a certain minority - but no-one can be sure that next time he/she will be part of an other "minority" of apple users.
@ apple: I AM NOT AMUSED!!!
Just do your software-job correctly and don´t spoil your resources in a ridicular way by "making the hardware 0,1 mm thinner" !
Holy Shxx!!!