My passport never used to work at the eGates. It took me ages to work out what might be the cause, but I realised that the Passport Office had seemingly 'flipped' my photo when making my passport - so my left is my right on the photo. I've no idea why this was done, but it was. Nor am I sure this is why it didn't work on the eGates.

But what I do know is that in more recent years, I have become encumbered with a significant amount of beard - and now the eGates work perfectly. It may be total coincidence, but I wonder if whatever the recognition tech is effectively ignores the now bearded parts and concentrates on, say, the eyes, where the flipping is less apparent. Honestly no idea, but I find it quite funny if it's true.