It's the bottom of the first digit on the rhs so 16 would have the bottom of the 1 missing. Just fitted a new zebra strip from rpi engineering and followed their youtube video. Cleaned the contacts until they were spotless using contact cleaner and wooden cocktail sticks. Put it back together and the above problem, so took it apart again and found nothing wrong reassembled and the same fault.
I did the strip because in the colder weather it lost bits here and there but worked fine once warmed up or the milder drier weather arrived. I'd like to say that all the pixels were there on a warm day but I'm doubting myself now.!
Is it possible one of the copper contacts isn't quite as spotless as I thought? Or maybe I should clean the new zebra strip with contact cleaner incase that's got something on it? It came stuck to a piece of card with sellotape which came off in one piece. Run out of time today but thoughts welcome before I strip it down again hopefully tomorrow.