ControlDoublePrivate::getControl returning NULL for ( "[EffectRack1_EffectUnit1]" , "num_effects" )

I use the following code section in my mapping:

 for (let macroFxUnitIdx = 1; macroFxUnitIdx <= 2; macroFxUnitIdx++) {
        let numOfLoadedButDisabledEffects = 0;
        let numOfLoadedandEnabledEffects = 0;
        for (let effectIdx = 1; effectIdx <= engine.getValue("[EffectRack1_EffectUnit" + macroFxUnitIdx + "]", "num_effects"); effectIdx++) {
            if (engine.getValue("[EffectRack1_EffectUnit" + macroFxUnitIdx + "_Effect" + effectIdx + "]", "loaded") === 1) {
                if (engine.getValue("[EffectRack1_EffectUnit" + macroFxUnitIdx + "_Effect" + effectIdx + "]", "enabled") === 1) {
                    numOfLoadedandEnabledEffects++;
                } else {
                    numOfLoadedButDisabledEffects++;
                }
            }
        }
   }

This worked without failure, using Main versions from ~spring 2021. Now I updated to the latest Main and get the following warning:
warning Controller ControlDoublePrivate::getControl returning NULL for ( "[EffectRack1_EffectUnit1]" , "num_effects" )
warning Controller Unknown control "[EffectRack1_EffectUnit1]" "num_effects" , returning 0.0
warning Controller ControlDoublePrivate::getControl returning NULL for ( "[EffectRack1_EffectUnit2]" , "num_effects" )
warning Controller Unknown control "[EffectRack1_EffectUnit2]" "num_effects" , returning 0.0

With return value 0, the loop is longer executed of cause, and the mapping does not work as expected anymore. The CO is stillin the manual for 2.4, so I supposeit should still work: https://manual.mixxx.org/2.4/en/chapters/appendix/mixxx_controls.html#control-[EffectRack1_EffectUnitN]-num_effects