Probable solution (I don't use Excel forms myself, neither I use Excel online):
You must have the column(s) in online Excel file formatted as Numeric/General;
Form field(s) you use numeric values must be formatted an Numeric/General. And in case there is VBA used for data input, be sure the data format is right one too.

In case you have in online file a lot of data with leading apostrophes:
1. Format columns meant for numeric data as Numeric/General;
2. Select range(s) you want to convert;
3. Activate Replace, into search field enter apostrophe, leave replace field empty, and click Replace All!