Rename by Regex not functioning as expected

I have strings in the following format;

guestfilesystem:F:|percentage SERVERNAME

I have a working regex query that should give me two groups, that essentially gives us the below;

SERVERNAME F:\

The regex that works (in any online regex tester) is;

guestfilesystem:([A-Z]:\)|percentage (\S+)

Output;

guestfilesystem:F:|percentage SERVERNAME
F:
SERVERNAME

However, this just doesn not work in Grafana. I do not get anything in $1 and $2. Where am I going wrong?

What I have noticed is when viewed in table form, it essentially gives me two columns; Time and SERVERNAME, where time contains the timestamp and SERVERNAME contains the % value of free space.

Underneath there is then a dropdown, containing a list of guestfilesystem:F:|percentage varients, whereby each choice is data for a different SERVERNAME. Obviously each SERVERNAME can have multiple guestfilesystem:LETTER:|percentage entries, where the LETTER changes.