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I think the DPC is likely to be directly above the air brick so the mossy brick is below the DPC and not a problem as such
That's what I was thinking too (not that I know more by any stretch - I just spend my time trying to fix damp problems).
What does the door frame look like on the side that has the damp?
If that's damp around the light switch, it suggests that water is running down the wire from somewhere - which means that it's possible travelling along a joist from somewhere else.
Someone probably knows more than me but I think the DPC is likely to be directly above the air brick so the mossy brick is below the DPC and not a problem as such. The patio also appears to be below the DPC. I'd be looking for other problems.