There’s another known fault that someone in the TfL overflow call centre recently admitted to me. If you miss the green missing light and pull the bike out a fraction too late, when you insert your key again the bike red lights. While you won’t be charged, the bike is unusable (and presumably drops off the data feed). Apparently ‘the system doesn’t know there is a bike there any more’.
How it manages to forget there’s a bike there, but lock it in, and know to red light it, is a mystery