First I thought it was Snapchat because I read somewhere that there are camera problems, so I stopped using it. From then I have made a factory and a master reset, rooted the phone and even installed CM 12. The only way to get it out of the boot loop is to connect it to a charger that is not a fast charger.
Then it starts charging and works normally and you can do everything normally.
Troubleshooting: When you said that the contacts won’t download I assume you’re seeing the message “Updating contact list…” and that you left the phone for several minutes to a few hours already.
Problem: My phone often got stuck at e boot up Samsung logo. Solution: You can actually just turn the phone off and on again and it should boot up normally provided that you’re not pressing other keys except the Power button during startup.
And also occasionally, it will show the green android on screen & below it states “Downloading target. At the same time, at the top left hand corner of the screen states a series of text with one of them saying “boot up failed”. If that won’t work then here’s one trick a lot of people think is absurd but very effective: Well, try it!
Your second option is to do the master reset again but this time, DON’T RESTORE your apps, instead, download fresh copies from the Play Store.
However, if the problem was fixed in safe mode, then it must be your third-party apps or one of them that’s causing the problem.