Hoping someone has some help/suggestions! Have a Panasonic sd-zb2502 breadmaker for about 3.5 years now. Love it and has made bread perfectly for ages. Usually use a granary/seed Wessex mill flour, menu 4, medium. Ran out so used waitrose love life crunchy mixed seed flour (red packet). Also opened a new Allisons yeast tub. Used both of these before and don't remember issues - but bread this morning half the size and like a brick! Making a new one now but just had a peek and looks the same 
Could it be the flour? Manual suggests this and also possibly humidity can affect? It is v hot in London today...or duff yeast (is there such a thing?). I'm irrationally put out by it, as it has always been fine and haven't bought bread in years (though will of course if have to, hungry DC to feed!)
Thanks in advance!