before the copy and paste,
/singlefiletest/test.xlsx was greater then zero bytes.
after the copy and paste,
Copy (1) test.xlsx are zero bytes.
if i kill the mount, restart the mount, both files are still zero bytes and excel is not able to open either file.
at first, i tested with a simple .txt file, non-zero in size, same behavior.
tho if i open the two texts files in notepadd++, both files open and are empty of contents.
since the OP was using a excel spreadsheet, i also tested with that.