I can vouch for the fact that I have observed shrinkage with the pink foam, which I think is the same substance, different brand. I had a shelf layout partially built and kinda gave up on it for several years. I came back to it the other day prepared to rip it out and redo and on close observation found that the rail had buckled in several places. Now mind you this was an all-foam shelf, 2 layers of 1.5 inch laminated together, no plywood. I did minimal rail gapping because I thought the foam was dimensionally stable, plus there are no temp variations in that room and we don't have humidity issues here. But the foam shrank and that was that. I measured it and found that the original 8 foot length had diminished by 3/16 inch.
My new shelf is going to be one layer of foam on 3/4 inch plywood but I am going to cut the foam every 2 feet so it can't mess with me again.