Are we talking about above the window just to the right of your extractor fan cowl?
If so, there would appear to be a vertical(ish) repaired crack above the window.
If that's the case I'd probably make that the starting point of my investigation.
that's it yeah. That is repair to cracks I have had done in the render 2-3 months ago as an emergency repair by a handyman I use. Before and afters here.
Nb this work isn't perfect but he was able to do it within a few days of the worst of the water, and it has helped a bit. Basically a plaster
2 flats above me, both with dry walls on that elevation with neither of them reporting issues