using an aftermarket part?
might need to go with OEM to stop that , we all know about sub-par aftermarket parts and the gamble we take when using them.

When i worked for Yale years ago we had a similar issue happening and they wound up having to change the pump mfg , they had switched to all aluminum pumps which is great for heat dissipation but bad for durability.
The new pumps they came up with had aluminum housings with cast iron end housings.
I was going to suggest the pressure relief being the issue but since you changed the adjustment to under spec that sort of rules that out and made me think of the part source and design of it.

and then there is the offshoot thought of if the units hydraulic system is being put under some sort of extreme shock by the operator. Oh another thought, hydraulic system accumulator? does it have one?