I have the same issue on my elipitical, dosen't register steps even using the handles for working your arms at the same time.
I put it on my ankle yesterday and did 2.30 miles and it registered 1.7 so it was a little closer but with todays technology I would expect better results. I haven't seen any response to my question from somebody representing Striiv as of yet either.
Do you still have that issue?
Have you tried opening a ticket?.
(click on "+ Support Ticket" on top of page to create one)
You should get a response fairly quickly - within 24-48 hours if I remember well.
I know that my Fusion Bio does not register steps accurately for any activities other than continuous walking of running (info found in the application).