Hi Becky,
I cannot reproduce this from my side when pasting data from a workbook. I had the experience that the data becomes ### in Excel and that will be fixed when I doublee-click the cell. You can try that too.
Here are two recommendations:
- You can try other options in Paste Special:

For example, if you need the data links to the workbook, you can use Paste(top left on the Home tab) > Paste Special > Paste link > Microsoft Excel Worksheet Object. This way when you need to change the data or the format, you can do that in Excel.
- If you want static data, you can consider paste it as a picture. Right-click > Paste Options > Picture.
For further assistance, can you share some samples of the files with us? You can remove all the confidential data. To share the file, you can upload the file to a cloud drive and share a link here. If the files are not allowed to share publicly, you can
share it via private message.
Regards,
Alex