One worksheet causes severe "not responding" delay on saving/scrolling

Sorry to necro this thread but the OP describes my situation exactly, and MS tech support have been unable to isolate the issue. By messing about for several days, discounting various things, I have narrowed it down to either an issue with the Workday function, or - more likely it seems - an issue with conditional formatting. Each cell has 4 duplicated conditional formatting rules, and the program hangs if I attempt to view all the conditional formatting rules for the entire worksheet.

How this actually happened is beyond me. There should only be two rules, one for column A and one for column B. How they got duplicated, why there are so many that it would cause Excel to hang/freeze can only be down to a bug. There's been no copying/pasting on this particular sheet, save for a row of formula that was done before conditional formatting was applied.

I don't know how to get out of this now. I'm going to try and copy/paste the values/formulas to a new sheet and delete this one, because that's the one thing I haven't tried.