Sound quality changes from time to time losing...

Question

my name is Robert Andrews and play regularly in church.I love my amp and have never overcranked.Sometimes it just seems to loose its tonal quality and kinda looses its presets without touching anything.I know it has a built in circuitry that supposed to keep everything sounding normal .I cant think exactly what the term used is but its in my book and i cant find it at the time.Theres nothing inparticular that is going on when this happens but it is urely noticeable when it happens.Sometimes it goes away quickly then other times i find myself readjusting to try to get my original sound.It just kinda looses its highs and its efx to an extent,hardly no vol. problems.I plat through a takamine supernatural with cool tube.Does the same with my others.Sometimes it wont happen for a month then couple times in an hour.Could someone please help me.All chords are top notch and have been checked Thanks praisethelord316