Hmm well that percentage is just a sum and should always add up to 100 as you said. I would ensure the format of collumn F is percentages and then look at the E collumn formula to ensure nothing was accidentally changed. You compare the cell formula to the original sheet in the link above.
If you just cant identify the issue then making a fresh copy never hurts. I do it all the time to troubleshoot :)
RE: Portfolio Rebalancing Tool Using Google Sheets - Quadruple Your Earnings!