@zurrain101

i also have this kind of problem before but i figure out how to fix it...it works on me'hopes it works on you too...

first regarding contact name in conversations...
this problem is cause by two thing...
1.the contact number = the best way to fix this to add +6 infront on the contact number...
2.call notify = if you have install this then disable the vibrate notification

second regarding you conversations disappearing...
this cause by two thing...
1.to many conversations in your phone = delete old conversation in your phone...if suddenly your conversation disappear then quickly reboot...
2.call notify = again disable the vibrate notication...

mostly this problem is cause by call notify...i disable the vibrate notification...i don't know if my method works on you or not but just try it anyway...