Conditional Formatting Question

I am losing my mind. I frequently use conditional formatting, but for the life of me, I can't figure out why it is completely unresponsive in this workbook. I use it all the time to highlight dates that are upcoming (highlight between today and today+30), things that are overdue, etc. In the attached workbook, I am trying to highlight column F with Highlight Cells Between =today() and =today+30. I can see with my own eyeballs that there are dates between now and December 17th, and they are stubbornly not highlighting!!! WHY?! But when I select "Highlight cells equal to" and pick a random cell, it works, so I know it's not like I'm working in a formatless void of a workbook - it CAN do it, it just....won't!!!

What I really need is someone to explain to me what is happening, why it's not working - I am less interested in someone delivering what I want. I can do it myself because I do it all the time - I just want to know why it's not working now!

Also, hopefully the attachment shows up. This UI from 1995 isn't exactly making me feel confident.