My guess is it the global warming issue again which is knocking the growing seasons out of kilter IMHO
I would say the toughness is down to watering or lack there off!
I see it as a similar situation to blossom end rot, which is also down to watering or lack there off!
Furthermore, I am finding I have to water a bit more scientifically than I did in the past.
In the past, I generally could tell if plants needed watering by how their leaves hung/lay.
Now that I now do a lot more containerised gardening, I can't judge the situation as well!
I have bought myself a combination moisture/light/Ph meter to help me decide!
With many of the 'modern' composts I find that the compost surface looks to be dry, so I water, where in fact I find my compost can be quite wet, and if I am not careful the compost can become saturated to the point it 'drowns' the plant because the saturated moisture prevents air getting to the root system!
But as I said this is OMHO