Al Nahda tower on district cooling — a couple of rooms lag and the FCU seems weak, what's worth checking?

Good instinct to check before escalating, and the pattern points home-side. With district cooling through FCUs, the quick tell is this: if only a COUPLE of rooms lag while others are fine on the same building feed, it's almost certainly those individual FCUs, not the district-cooling supply, a clogged coil or filter, a blocked condensate drain, or a stuck control valve/strainer starving that unit of chilled-water flow. If ALL your rooms went weak together, then you'd suspect the building supply or your flat's main valve. Since it's just a couple, start with the FCUs: are their filters clean, is the condensate draining, do they blow much weaker than the good rooms. A service that cleans those FCUs and checks the chilled-water flow to them usually restores the lagging rooms without any need to involve building management. Getting a water chiller service in Dubai that understands FCUs to meter the flow to those specific units confirms whether it's the FCU or, less likely here, the supply, so you're chasing the right party.