[booklover]

I have grown tomatoes in large pots in my greenhouse in the same way for donkeys years.  Normally they keep growing until I need the greenhouse for overwintering geraniums etc.  This year they have started dying, the leaves on nearly all plants went yellow and they stopped producing fruit in August.   The only thing I did differently this year was to give them some Epsom salts once (One tablespoonful in 5 litres water).  Usually we set up automatic watering but because we were not going away this year due to lockdown we hand watered.  Could the hot weather have 'cooked' them? It was very hot in the greenhouse even though it is shaded.  The varieties were Sungold, Gardener's Delight and Beefmaster and they were all affected.

[Yorkie]

I think it's entirely possible that the hot weather could have impacted on their growth along with the absence of automatic watering.  There's always next year!

[8doubles]

A wild guess i would say overwatering .
Underwatering they would wilt first but respond when watered .
Blight would send them brown .
Your epsom mix is the same as i use .

Provided you did not use the weedkiller can when watering i would say just too heavy on the aqua.
A finger in the compost is a reliable indicator  , if still damp leave them be.