I don't know if anyone else has run into this issue before but I just stumbled on this today and it had me baffled for about an hour.
So on occasion I will throw an adjustment layer into my composition as a holder for expression controls, this works fine since adjustment layers dont actually do anything unless they have an effect applied. So today I needed to modify a part of my expression driven animation (a very simple text write on) I proceeded to duplicate my text and the adjustment layer then update the expression links on the text layer. When I changed my slider values on the new adjustment layer I noticed they were changing the values on the sliders in the adjustment layer below it. If I duplicated a slider, it was duplicated on the new adjustment layer as well. I was really baffled.
The only explanation I can think of is that since the sliders are on an adjustment layer, the top most layer is driving the values on the sliders below. Not sure why the duplicated sliders also show up on the new layer but at least I have a rough understanding of the issue. Since this was such an obscure issue I figured I would share with the community.
So the lesson is never to use adjustment layers for expression controls.
X = text.sourceText;
F = Math.round(time * thisComp.layer("Null 21").effect("Blinking Speed")("Slider") % 1);
L = X.length;
T = time * thisComp.layer("Null 21").effect("Speed")("Slider") - thisComp.layer("Null 21").effect("Start At")("Slider") * thisComp.layer("Null 21").effect("Speed")("Slider");