As with any major change to software some people may experience some issues and with Apple Music that has occurred.
I personally have had no issues and think Apple Music is a great service.
One of the biggest issues that people have contacted me about is the syncing across multiple devices has stopped working , such as you create a play list on one device and it does not appear on all devices.
The quickest fix for this has been to sign out of iTunes on your devices and then sign back in.
Apple this week have released an update to iTunes ( Apple Music ) that fixes other issues.
More information can be found below:
A great article from Serenity Caldwell over at iMore should answer all your questions : Troubleshooting Apple Music : The Ultimate Guide