You are experiencing something called gimbal lock I believe. To avoid this problem I would use the node Combine Rotators. Instead of breaking and making, create a rotator that represents the offset per tick and then add it to your static mesh’s rotator.
I’m struggling with rotating an actor by pitch 90degrees at a time and cannot get past gimbal lock flipping at 180. Could you explain how the example above applies. Maybe show a blueprint example. For all other rotations I’m breaking and making a new rotator and then using SetRelativeRotation. Please help.