i would bet on the scope or mounts or rings.

the hot temps shouldnt have such an effect...should still hold a group even if it was somewhat off from before...

check it out and see if you cant find a loose screw or something.

then if that dont help id have the scope checked. could went bad. ive had it happen. i had one that every time you changed the scope power the crosshairs randomly moved and never moved back..it was all over the place. junk scope though...thats when i quit using junk scopes.

then if the scope checks out id take the rifle to a gunsmith or call the rifle manufacture..

just take YOU(shooting poorly that day possibly or something to that extent?) and the scope/bases/rings out of the equation.

could be a number of things...check them all out and see if you cant find the culprit...good luck