I was looking at the Vueling website recently and I have noticed that the site is now showing flights for late June 2019 onwards.
I know that among many other places they have flights between Malaga and London.
At present it looks like they have filled in the calendar of flights for the period through to the middle of October 2019. However if you try to book any flights after late June they are currently unavailable to book. So my guess is that they should be releasing these flights for booking pretty soon.
Perhaps they release flights for different routes at different times over a period of time to reduce load on the booking part of their website.