From a developer:
If the same key is mapped to N action events all the mapped events fire N times.
This issue only exists with the OpenXR plugin enabled and does not occur for any keyboard/mouse input keys.
We have tested and replicated this issue on the following
Oculus Quest using Oculus Link
Samsung Odyssey via Windows Mixed Reality
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-119670 in the post.