images randomly pixelate on export?

A game I made in Unity just got on the app store today. (search for Demonfall) When I installed it on my iphone, I noticed the lava animation was pixelated. It seems to happen randomly. I remember during development I exported to apk to test on my Andriod and one of the demon's arms animation was pixelated. Re-export and it was fine.

Is there a way to stop this random pixelation from happening? My plan at the moment is just to reexport and resubmit to the store

 

so... I fixed the lava animation by setting it to 'truecolor', reuploaded to the app store... and now all the other animations are pixelated -,- I'm just going to set all animations to true color, it's a performance hit but I don't want to have to resubmit to the app store again...

 

.....even after setting it to true colour, some of the sprites still are pixelated....

wow, this is getting annoying