Thanks Yak.
So it was the bleed valves diaphragms and nothing in the FCU.
I had one going bad right after takeoff in a B200 (-42s) many years ago (1994-5ish) and I remember that power dropped by roughly 700ft/lbs whilst ITT rose. The yaw was considerable, but not unmanageable. (but that happened in bright sunshine...)
After reducing power to appr.1200ft/lbs IIRC ITT was 740° which was our company ITT limit, we limped to our mx base, fortunately only a 25 min flight away. After a boroscope inspection and a new valve installed the engine was fine again.