This phone easily records conversations. Check in your audio then go to voice recordings. I guarantee you have accidently recorded a conversation and it wiped out your memory. I had this problem and finally figured out what was causing this. Just delete it the recorded conversation and you will be fine!

This happened to my phone too (ease). You have to delete stuff you dont need, for example (like i Did)..i deleted pictures that i didnt want and old ringtones. Empty out ur inbox and all calls in records..

Hope this works :)