You're on the right track so far.
Take the rifle apart and clean up the latch and shelf real good.
Is it popping open sometimes and staying latched but hard to open other times?
On the times when it's hard to open it probably tried to pop open but didn't quite make it... it flexed just enough to make the latch bind up a little.
The latch and shelf will take some time to mate to each other and smooth out.
Cleaning the shelf might be enough to fix things. In any case it's an easy fix.
Most importantly... Welcome to GBO.
Spanky