Tomatoes - Blossom End Rot

[Multiveg]

Up until last year, I don't think I had ever seen blossom end rot on my tomatoes... Been growing tomatoes for ages... even neglecting them for a few days when away visiting, filling up the drip trays to the brim before leaving... tomatoes happy for years... but this and last year... well, we've had heatwaves,... is this a sign of more issues to come?