Had similar situation in my kart this weekend. A couple things helped and my thought process (I am still learning).
Dropped tire pressure from 11 lbs to 9.5 front and 10.5 rear. ( the fact that it handles well for 5 laps then goes off on a 90 degree day tells me this could be an issue).
More negative camber
I could have widened the rear, but I was already at max.
Also a stiffer front torsion bar (I didn’t have that available).
Also possible to widen front track?
Maybe raise front of chassis?
