Add me to the list of affected users.
Just turned on the 3 months Apple Music trial (family option).
Library of 36k songs on iMac.
Had to re select update library for uploads to being in the first place but uploaded around 15k songs within hours (thought that was quite good / fast!).
Have not turned on Apple Music library on iPhone - no problems.
iPad (4th generation), turned on, trying to download around 15k songs.
Whole iPad experience has now slowed down to being barely usable.
Can't seem to switch off the Apple Music library now - keeps going!
Given that I haven't switched this on, on the iPhone, I guess I will either wait to see if this gets fixed or I'll never be able to sync a new track to my iPhone unless I purchase it from iTunes which makes a mockery of paying for Apple Music.
The whole experience works beautifully on my 4th gen Apple TV, and my kids and wife can do what they like on their devices, so there are benefits, but also quite a lot of pain!
Not impressed.