Google Sheets Timeline - Conditional Formatting not working :(

Hi all,

Just wondering if anyone can help with this... I have previously built interactive timelines using Excel & Google sheets that incorporate conditional formatting based on START & END dates based on 2x cells.

For some reason when I've tried to put a new one together the conditional formatting does not seem to be working.

The formula I'm using is;

=AND(S$8>=Q$10,S$8<=R$10)

Which is applied to the range S10:RH1999

As far as I can see this SHOULD work, any help here would be much appreciated!

Thanks
Jack