Checkbox help - Box won't check/uncheck when linked cell formula generates true/false

I have a workbook set up with a Home page. When the user check that an option is desired (using CheckBoxes), then the worksheet with the matching Caption name will be displayed. When unchecked, the captioned worksheet is hidden. Because choices of which worksheet should be display varies based on the state selected, some of the choices must go through a true/false logic. All of my checkboxes are working correctly, except my newest changes.

My true/false logic is displaying the desired result however it will not check and uncheck my linked Checkbox. when I clear the formula out and start over, it will work one time (and one time only). e.g. a fresh formula will check the linked checkbox when the formula is true, but when I change the variables generating a false in the linked cell, it won't uncheck the checkbox. Did I accidentally delete some VBA code which controls this? see screenshots.

display of CheckBox26 Properties: checkbox 26 true.JPG
true/checked: checkbox 26 true formula result.JPG
false/still checked:checkbox26 false formula result, linked cell still checked.JPG

Thanks for the tips. I finally managed to solve my problem. Once I simplified my vlookup to exclude nested if/thens, my checkbox started working fine.