If I turn on the visibility for all bones and bone layers and search for the pattern “CTRL_armSpline.001”, I only get “CTRL_armSpline.001.L” and “CTRL_armSpline.001.R”. It seems that somehow this “Driver” data block marked with the red line in your screenshot above “survived” the renaming and is now useless. “CTRL_armSpline.001.L” and “CTRL_armSpline.001.R” by the way don’t have any constraints or drivers. I’ll delete this broken driver and test the rig afterwards.
