Are your downlighters insulated? Should they be? When you last had an upstairs bathroom replaced, did you fit downlighters and if so, did you replace the loft insulation above it?
For loft insulation to work, it needs to be thick (think 11-12 inches, 270-300mm), uncrushed (no good if you store currently unused stuff on top) AND unbroken - if there are gaps or holes most of the benefit is lost.
However, downlighters get hot, even LED ones and should not be covered by insulation. I just had a bathroom done and the electrician left most of the insulation in a heap in the corner of the loft, with the bathroom ceiling almost completely uncovered and he was upset when I covered his newly fitted downlighters.
So what should you do? Well, lets not get technical and avoid talk of fire chimneys and whether you need fire hoods or not, whether you have bulbs or integrated units - each have slightly different needs - but the simple solution is to fit a 'Loft Lid' or similar device over each downlighter (think of it as an upturned flower pot without the holes). This gives room for the heat to dissipate but you can run the loft insulation over the top without losing its benefit. Just search for 'downlight cover' for examples.