LONDON (Reuters) – British Airways said on Friday it was working hard to resolve a technical issue after its website and app appeared to be down, adding that it was still checking customers in and operating flights. Users on Twitter posted messages asking BA when the problem would be fixed however, with one man showing a video of lengthy queues at the check-in desk for what he said was a Miami to London flight, while another user posted pictures of blank screens. “We’re investigating and working hard to resolve a technical issue and apologise for the inconvenience,” the airline said in a state…