My POV, I do not think a heatsink thickness, would cause your problem.
More towards a electric heat power surge / bad solder joint etc.
I have 2 SF 4000 from 2019 from the E-bay store USA.
Board thickness is using a Mitutoyo Absolute Digimatic Caliper:
0.1180 inches / 3.00 mm.
It is not cost...