attached is the file I pulled from the main source, but the issues are the same - see the highlighted $0s that should be sums ps - there is no paperclip on my end.

Okay, so there was a circular reference. Let me explain. The formula in cell C18 was =sum(c13:c21), so excel is trying to sum cells C13 through C21, including C18, where the sum is going. Everytime it sums, C18 updates, so the formula must update, so C18 updates, so the formula updates, etc. When you tried to sum C18 and C19, Excel just gave up, because it can't really compute C18. If you change the sum formula in C8 to sum C13 through C17, =sum(C13:C17), everything seems to work.