I can tell you the most common reason anyone ever goes out of tune, is do to sloppy winding of the strings around the tuning pegs. If you have ANY slack or slop there, it's going to slip and go out of tune. Make sure you keep tension on the string as you wrap it around the peg and wind it up.The neater and cleaner it looks, the less it's going to slip and go out of tune.

Another common mistake is not "tuning up". It's always better to tune the string up than down. When you tune up, you're tightening the tension. If you tune it down to a note, you've loosened the tension a bit, and it may not hold as well. So if you're tuning, and you go too high, you need to go way back down, start over, and tune UP.

And remember, tune all 6 strings, EVERY TIME. Every time you change one string, it will affect others. So tune all 6, check them all, tune them all again, until you're happy.

A lot of times the stock tuners on a Gibson/Epiphion are pretty cheap and don't hold that well.
Although I'm not a fan of how they make the guitar sound, Grover tuners do serve their purpose and generally hold tuning well. So it's entirely possible that that fault may lie with you.