Thank you for the replies.
This is what I know so far:
1. Workbook calculation has been and is set to automatic, although I checked it while searching for answers online.
2. The file isn't that large or complex and my computer is powerful enough for Excel to not be a problem at almost any level of complexity, although I did wonder for a moment if it was a driver problem.
3. My conditional formatting rule is basically (=J2="Incoming" then strikethrough text) and the same for another cell, just a different word. I made sure to keep it simple.
edit:
Apparently this is quite an old Excel bug (I've seen references to this starting with Excel 2007). People aren't entirely sure why it happens.
So, trying the same conditional formatting on a new file results in the cells updating immediately, which is confusing, as the original file, as I stated before, isn't that complex (6 sheets with not that much data, formulas or code on each one).
After searching online some more, I found a workaround here.
Basically, all I needed to do is add this to the sheet's VBA:
Thankfully I didn't have other code running for that sheet.
SMH
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