Error 0x1003 (No free space) on nearly empty 8TB external drive.

Hey everyone, I ran into an issue today trying to backup data from one of my externals to an identical new one. I had no problems backing up my PC to my first external, but now I want to backup the backup and about a Tb of other files from that external to my second and I'm running into an error. Whenever I try to backup any files/folders to that drive (regardless of size), I'm presented with:
Description: Scheduled Backup Failed
Reason: No Free Space (cannot create partition of requested size)
Error Source: Paragon Backup and Recovery 2017
Error Code: 0x10003
Backing up 50Gb-1.3Tb folders to a nearly empty 8Tb drive shouldn't be giving me this issue, so does anyone have a solution?

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