Apps are automatically closing/restarting and phone is running slow
"The problem is that under certain circumstances Android 5.0 and 5.0.1 leak memory, and when the leak has reached a critical point then Android tries to compensate by forcibly closing apps to free up resources. What the out-of-memory killer doesn’t know is that it is Android itself that is leaking the memory and not the apps."

http://www.androidauthority.com/fix-lollipops-massive-memory-leak-coming-soon-ish-577101/

It is an Android lollipop bug. It should be fixed with the next update.