Basic rule about track is if the rail is moving, you're going to have trouble. Almost my experience with sun kinks has been on Class 1 or excepted track.

Pull-aparts (stripped joints) and some broken rails result when the rail has contracted (generally due to cold weather) and either the bolts or the rail itself gives up. Sun kinks are due to the opposite - heat has caused the rail to expand, and the track structure must hold the rail in appropriate alignment. Sun kinks generally occur in the weakest point of the track structure - either bad ties or an insufficient ballast section. Curves already offer a direction for the rail to move to the outside.

When jointed rail is laid, the gap between the rails is varied with rail temperature. Welded rail is heated to a specific temperature, then vibrated into place before rail anchors are applied. The clip systems (concrete ties) also acts as anchors. These are standard procedures to limit rail stresses.

It doesn't matter if rail is welded or jointed, sun kinks can happen in either case. I don't recall ever seeing a sun kink just because of one welded rail, but I did stop for a single rail sun kink on 72# jointed rail that went vertical about 3 feet high and lifted the opposite rail almost the same. The track gang had to cut out about 9 inches of rail to get us over it (after knocking a joint apart to get the track to drop), and then cut out more to permanently repair it.

My record was a couple summers ago working as a temp engineer for a shortline with mostly 90# welded rail on bad ties - both in derailments (often due to sun kinks) and sun kinks themselves. If you run long and heavy trains, loads primarily in the same direction, where the rail is moving on bad ties during the heat of extreme temperature changes - get ready for sun kinks! That is why many shortlines and branches with poor track limit loaded trains to nights and about 30 loads maximum.