Sure those faders had the same level when got paired ?
They keep relative level to each other.
A double click onto the fader let jump it up to the zero position.
Make both up to zero, then create the fader group.

Setting them both at 0 solved the problem! No mention of this in the manual

Groups. The area Groups provides 4 storage places each for fader, mute and
solo groups. The groups are valid per Workspace, being active and usable in
all 8 Snapshots. But with this they are also lost when loading a new
workspace, in case they have not been saved before in a different
Workspace.
Note: The Undo function will help in case of an accidental overwrite or
deletion of the groups.
TotalMix uses flashing signals to guide you through the group setup. After a click on Edit and
click on the desired storage place all desired functions for this group have to be activated or
selected. The storage process is finished by another click on Edit.
When setting up a fader group make sure to not add faders that are at the top or low position,
unless all faders of that group have this position.
The Mute groups operate – other than the global mute – exclusively for the current routing. This
way you can not mute signals on all outputs unintentionally. Instead signals can be muted on
specific submixes by the push of a button.
A solo group operates exactly like the global solo, signals outside the current routing are not
affected.

That's the entirety of the manual when it comes to fader groups.

Appreciate being able to have folks answer questions here that aren't easily found in the manual or online anywhere that I can find.