WARNING: Filename "C:" contains ':' which the operating system does not allow in paths. Replacing ':' with '_' and appending hash

I get this warning in my logs every single evening.

These are my exclusions:
D:#TEMP*;D:\VirtualPCs*;C:\Windows*;C:\Program Files\WindowsApps*;C:\Users\victo\AppData\Local\Packages\TeamCherry.HollowKnightPC_y4jvztpgccj42*

These are my directories to backup:
D:;C:\

Any ideas?

I’m running Windows 10 and only backing up the local PC.