before the copy and paste, /singlefiletest/test.xlsx was greater then zero bytes.
after the copy and paste, /singlefiletest/test.xlsx and 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.
This problem stems from the way the Windows Explorer works with file system. I don't know details but the way must be rather dumb.
If you install TeraCopy (great stuff btw) and configure it to handle file copy/pasting by default, the problem goes away. TeraCopy internally starts from creating a temporary random-named file and renames it to the final name at the end after success.
I noticed this in 2019 but had no time to dig deeper. You'll want to copy/paste a file inside the same folder and look very thouroughly at the VFS log to understand the quirk. I guess that the solution might lead to a new VFS mode that buffers full file during writes. At any rate, this quirk deserves a paragraph in rclone docs!
The issue #2187 mentioned a similar Windows Explorer quirk: when it creates a new folder, it makes 4 retries if it doesn't like something in a result returned by the file system.
teracopy is good, but not closed source and has the free edition and paid edition.
so i use fastcopy.
also, using double commander, dual pane file manager, these ms-windows bugs do not happen.
i know you are super busy behind the scenes but...
these two issues prevent a huge amount of windows users from being able to use rclone mount, not being able to perform basic operation, copy and paste.