We know gradebook exports aren't perfect and until we get that fixed we wanted to offer a solution to help calculate based on percentages.
Step 1: Add a column the right of each Assessment
Step 2: Copy/Paste one of the two formulas below to the newly added column. (Note: You'll need to adjust A1 to the cell to the left and then drag down to cells below)
Step 3: Copy all values in the column > Paste special > Paste value only to remove the formula and be able to calculate based on the raw numbers.
Once you have the raw numbers you can delete the original columns so that you're only calculating based on what you need.