I'm seeing odd patterns in plant health in the UK, despite being in one of the best fruit and veg growing areas in the country.... my observations:

a) Garden centres are selling compost that appears much lower quality than last year and that doesn't hold water as well, it also has much more perlite/vermiculite (or something else?) in it,

b) We've had MUCH better sun than last year - when I had a bumper crop - but this year both plant chlorophil and produce levels are 50% down. I've been providing plenty of seaweed, tomorite and manure but it's having little effect? Typical summer temps here are 15 to 25 degrees but we've had 25 to 40 this year - so why aren't plants producing?

c) Plants that usually overgrow are even more reduced in size; mint, perpetual sweet peas, raspberries, rhubarb, courgettes,

Composts in the UK are all going peat free. As a result they seem to be higher in Nitrogen and producing leggy plants and no produce. Our veg was all pretty crap this year and my pumpkins didnt even pollinate.
However my parents bought some soil from agricultural land as they had a few large beds to fill and their produce results have been crazy. Big lush vegetables, huge onions and garlic, a large potato yeild. Seems everything they plant in it grows really well.
I'd like to get some of the soil myself but its costly and my location is not very accesible.