Mine has this problem, it has not worked for several years.
I always ask and quite often they say 'oh its a fault' or 'I don't know' or 'it's your technique in the machines'. A few weeks ago someone told me "we are looking for someone with your name". Today - I found a friendly border officer in the "seek assistance" lane and asked again why it never works, he offered to check it out. He told me "your passport works fine, you are fine, but it will never work in the gates. You always have to try because it shows up on our screen if you don't". When pressed on the reason he said "you have a common name, that's all I can say". So I assume correlated with the earlier officer saying they were looking for someone with my name, I'm thinking that's the reason.
Here's hoping they are caught soon as it's inconvenient as a regular international commuter.