Hi stephanSLM,
This is most likely a system partition with hidden files, which probably is why it's populated but you can't see the data on it. I recommend you remove the mapping.
You will need to remove the drive letter and mount point in DiskPart in order to do this.
Hit Windows key + R together to go into Run. Type in the following: diskpart
Enter the following in the new DiskPart window.
list volume
select volume E
remove letter E
I hope this helps. Please do let me know if this fixes it.