Hi Simone,
As the error specifies "xdat vector is the breakpoint, which must be strictly monotonically increasing.", which means that the w_OOL data should be increasing as well as should not have any repeating data for it to be classified as "strictly monotonically increasing".
From the graph you shared it is visible that w_OOL data which has the velocity vector has multiple data with same velocity values because of which this error is arising.
To overcome this error you can either create a look-up table with Torque vector as the "xdat" or find a way to eliminate the repeating values in the velocity vector.