[Solved] Scrollbar Unresponsive

I'm having some trouble figuring out why the Scrollbar I'm trying to use refuses to respond to mouse input. When I click and drag the interior content of my Scroll Rect, the Scrollbar reacts, but I get no response from the Scrollbar when I try to click and drag the Handle. For the life of me, I can't figure out what I'm doing wrong. I've gone back over several tutorials, but don't see that I'm missing any steps...

I've created a panel with a Mask and Scroll Rect component, assigned the vertical Scrollbar to the appropriate slot, and have my desired Content assigned to the appropriate slot. The Content itself is an oversized panel that is a child object of the Scroll Rect object. The Scroll Rect itself functions as expected, but the Scrollbar does not.

I've tried reparenting things, moving them around in the hierarchy, making elements don't overlap, and anything else I could think of, but to no avail. If you have any ideas, I'd really appreciate your suggestions. I've been racking my brain for a couple of hours now and have only succeeded in giving myself a headache.

 

Update: Still unsure exactly why that last one didn't work. I tried rebuilding it from scratch & the new version worked just as expected, even though it was set up just the same as the one before. Once I had a working prototype, I cannibalized what I needed from my original attempt and now have something that's almost what I was after... *shrug* Whatever works, so long as it actually works.