I am not sure this is a bug. In a Live Dev Q&A from 2022 (see below), they explained how Live Weather works, METAR injection is only few kilometers around the airport. So 5nm that are about 9kms seem right to experience a transition between the pressure coming from the METAR and the one coming from Meteoblue. The larger the difference is between both, more chance to get a quick transition.
Continuing the discussion from Live Dev Q&A - August 18th, 2022: