I’ve never used these nodes before, but looking at your images the decimal and thousands separators in your excel workbook and the text formatting string are different (the formatting string uses thousand separators with comma, decimal with period; whereas, your worksheets are period for thousands separator and then comma for decimal).
The first column you have a period in the numbers, which Excel will pick up as currency format, whereas the second column does not, so picks up as a general number.
Don’t know if that is your problem, but it is what I see.
Your suggestion will help. But you will also need to change the locale settings for your computer to match the environment of the OP. I’m not sure to what extent KNIME nodes are locale aware and in sync with the host operating system. We’ve always standardised on commas for thousand separators and periods for decimals to avoid problems, but that doesn’t apply to everyone.
The column in question is set to string instead of double. If you can’t convert it to double, then try to remove the commas first with Regex replace. If there are problems converting to double after that, then this could be a character encoding issue.
I found and solved the problem.
I put another String-to-Number node in front of the Excel writer node and converted the Commission € column to double format. After that, the XLS formatter nodes output everything correctly.