Maybe the SIM card is moving inside the tray. I remember I had a similar issue with the Note 2 and it was because my tray got bumped up at some point and the card was a little loose. Here's how I fixed it BUT take it with caution, as there is risk of damaging things further. I used a business card and cut out a small strip the same length as the card, then inserted that along the card (but being careful not to cover the metal contacts). That put some pressure on the card so it wouldn't move around. If it feels too tight to insert, though, I wouldn't try that. Also note that after I did that, it was MIGHTY HARD to get the card out. Had to use tweezers and everything, it was a PITA. So again, use with caution.
Facebook
Twitter
Instagram