Fishy, indeed. I worked on a contract to deliver fifty 1500-2500DWT short sea ships to Iran during the Iran-Iraq war. All of these ships traded mostly in the Baltic and North Seas, and few ever sailed south of Bordeaux.
I had worries as to how they would perform in the Red Sea and Persian Gulf with water temperatures of 28C-32C. However, in nearly every case, the heat exchangers were adequate once the regulating valves were opened up. In the cold seas, the jacket water pump bypasses were opened to reduce flow through the exchangers and keep the jacket water temps high enough. The ships were designed to operate world-wide.
The only trouble I encountered on some ships was that the turbocharger after coolers did not drop the charge air temperature sufficiently, but I was only delivering them to parties who likely did not know the difference, so I made no effort to correct that.
In the case of these RN ships, it does seem that the overheating could be easily addressed by installing larger or additional heat exchangers, which are available off the shelf or can be fabricated at no great expense. Navies, however, are not so keen on simple solutions.
That said, I would like to think of mil specs as robust.
I'm not a ship guy but seems that if the heat exchangers were insufficient in warmer water they could still function at a lesser load? I think they have a large turndown ratio.
The article makes it sound like they were dead in the water?
cuts out in warm seas, leaving sailors stranded for hours in total darkness
These are gas turbines (from an earlier comment).