Hi Steve,
If the 1st stage cylinders are not causing a drop and it is linked to the 2nd stage cylinders then it may be just a seal set in them or a blocked open poppet valve in the cylinder.
Combilift has a simple procedure to test if it is the valve bank, or mast. If mast, then what cylinder is causing the issue. You will need a gate valve.

For free combilift Support you can submit a ticket at https://warranty.combilift.net/technical-support-form/

Hope this helps.