Naming settings - Produces invalid file names on Daily Episodes

[DiesalZA]

Sonarr version: 2.0.0.5228
Mono version: 5.12.0.226
OS: Docker Container from LinuxServer (Host system is Debian)
Debug logs: Link - Google Drive (sonarr.debug.txt)

Description of issue:

Using a fresh install of Debian and the latest containers from Linuxserver, I am experiencing the following issue when trying to configure the naming options in Sonarr:

I haven’t done anything differently from what I’ve done in the past - and the issue appears on both Debian and Ubuntu 16.04 & 18.04 (I am using a container so I suspect it’s not the host OS )

Docker container logs display the following: https://pastebin.com/nhPD5fLS

Please let me know if you guys need more info

Thanks in advance!
Edit: Do I need to still create an issue on GitHub?

[markus101]

If you turn on Advanced Settings what is the Daily Format set to?

[DiesalZA]

I’ve left everything on the defaults:

Now, I’ve changed it to the following and it works?

So now I’m not sure what is the root cause - here is the debug log up to the 2nd change.
Google Drive