Curious if you have found a solution in the meantime? I have similar issues. The motion matching stuff works, but traversal has this strange vertical offset.
For future references:
After some web searching I found this video:
Retarget GASP Motion Matching + Traversal Animations Part1
It explains in detail the steps you need to use UE5 character with GASP. It also addresses this exact issue (starts at 11:12).