scooby L

I'm getting a brief flat spot/hesitation on 3/4 throttle at about 3,200-3,500 rpm (combined with a hiss/whoosh), followed after a couple of seconds by a jolt when the engine finally picks up.
This is only happening when the engine is warmed up, when it's cold everything is fine.
I have a SECS1004 monitoring the peak boost and this is showing 1.2bar when it happens, so I do not think it's overboost.
Has anyone got any ideas?
(The car has a de-cat downpipe plus green air filter.)
One theory could be fuel starvation, or is it bad fuel on the last fill up?
Cheers for any input