So your "y table sandwich" is the following, from bottom to top?
- aluminum
- cork(?)
- heat pad
- glass
I wonder if that "system" is just simply more responsive/compliant than with the wood. It fixes the big warping problem, but is more prone to the cycling error.
FWIW, I looked at the hysteresis management code in Marlin. I'd swear that my system operates exactly like the code would have it, if it were enabled..., which it supposedly isn't. Just the same..., it's a very dumb implementation, and not particularly tuneable..., doesn't seem worth fiddling with.
Enabling PID on the other hand seems like the way to go, maybe especially with an aluminum table.