Why is my phone acting up?

[AC Question]

I recently updated my Galaxy S5 to 5.1.1. Since then, my phone would randomly freeze and lag. I'd press the power button to lock the phone, and the screen would stay on for 10 seconds then a slow locking animation would occur. I press the lock button again and the screen stays off for quite some time. I already cleared the cache partition, but the same thing keeps happening about 3 or 4 times a day. What else can I do?

 

[B. Diddy]

Welcome to Android Central! Try booting into Safe Mode, which temporarily disables all 3rd party apps. https://support.t-mobile.com/docs/DOC-10696

If the problem disappears in Safe Mode, then something you installed is causing the problem. You may have to uninstall apps one by one until the problem disappears. If the problem persists in Safe Mode, then it's more likely to be a hardware or firmware problem.