Rear shock looses air but later regains it???

Hello, I recently bought a used 2015 Ghost Kato 3 off craigslist, and i took it out for the first time on a ride yesterday. when i would look down later during the ride, it would appear that my sag was at about 70%, rather than the 20% i set it for. My friend confirmed that it was much lower than it was than when we left the parking lot. after I noticed this, we decided to go back to the car and pump the shock again thinking that the shock may be leaking air. This did help it, but the psi seemed much higher than it was when i originally set it up. we headed back out, and hit some fairly technical trails, and on our way back, I noticed that my shock was really low again, so we headed back to the trailhead and packed up. Now this is where things get weird, once i got home after about 2 hours and took my bike off, the rear shock felt just fine and was at about 20% sag... Anyone know what could be the possible problem? Thanks.