Well that goes back to my original argument doesn’t it, ply is not a good substrate, period, even if it is overlaid by cement board, jackoboard, whatever board. It’s just poor.
It’s totally unstable.
But the best way to ensure longevity is to prevent deflection, and with ply, the best way is to use two layers.
If there’s no deflection it reduces the risk of it debonding ten fold.
Single layer ply still has deflection to an extent, that’s why it’s good practice to use an alternative, especially one that is inert.
Do you know, I’m sure there’s a couple of products out there that fit the bill.