I have my pint for only 3 days, but I was getting similar issues. I'd step on front pad and it wouldn't engage like half the time. It's always the toe area for me. But when I tried at home barefoot on carpet, I'd have no issue. This was true for me and my son.
Then I switched to Nike SB shoes which I already had and no issues anymore. I think it works much better with certain shoes. My son loves riding the Pint, but he's getting very frustrated with the sensors ... He doesn't have flat shoes, so I might try sticking something on the toe area.