getting movment in 4th axis when clamping

this is on an ooya re-5m, the 4th axis, called w-axis, is the bridge axis and is counter balanced . control is a fanuc 11m, with ac servo's .
I wanted to ask a question on our re-5m,
Concerning the w-axis,
When going from unclamped to clamped, I am getting movement in the axis, can see the output shafts (shafts coming out of gear box) on top of the bridge move, up to a half turn, sometimes less.
Diagnostics 3000 (servo error) will have a deviation value of up to 585 for the w-axis, it is not consistence,
But will go to zero if you unclamp the axis, ( as the servo turns back)
On powering up the nc, the axis’s are clamped. Diagnostics 3000 is 0.
If you unclamp axis, the diagnostics 3000 is still at 0.
But when you clamp the w-axis again, you get the deviation, and an actual movement in the axis,
Because this deviation is outside the window of parameter 1827, inposition width
The inposition check, diagnostics 1000 ,becomes a 1.
Have physically checked the clamps, all are working, moving ,hard to tell if they all holding,
I know when you clamp and unclamp, the clamps clamp and the servo brake cycles,
So don’t know if it is a physical problem of the clamps holding, or a servo problem.

Years ago, I ran an SNK RB4N bridge mill. The W axis was not numerically controlled, but had to be adjusted by a manual jacking motor. Of interest is the fact that when lowering the bridge axis, you had to go BELOW where you wanted to end up and then the sevo pulled the bridge UP by about and inch.

Maybe your control is trying to do something similar which could account for the movement you are seeing.