You have to re-zero your load weighing.
It's been a long time,but there is a rotary switch in the cop that you set it up with.

if there is a COP1 board in the cop, then there are some pots that need to be adjusted, you hook up to the correct test points and set the voltage with empty car according to the adjustment procedure. this has worked for me a few times, it is fairly simple adjustment. If it is a COP2 board then the procedure is a little more complicated, you access the cop board dip swithces, and follow the info displayed on the PI, you need weights. on the cop1 board, i have only touched up the empty car pots, that has solved my roll back problems, but there is a complete procedure for the set up from scratch, weights also needed. last but not least, you could indeed have a failure of the load sensors, or the isolation pads.

Thank you. This has indeed helped

null amp card? IAN pot test point to ground. set to 0v at rest with IAN pot
CLL pot clockwise to get rid of roll back.
cop1 board- tp 2-tp 6 = 0v with empty car via r45
tp 7- tp 8 = 0v via r49 with 75 % load.