Yorkshire Tea make several kinds, could be the wrong one?
Out of date box?
Milk gone off? Or wrong kind of milk. Or even just changes to its taste, I read milk tastes different with the seasons?
Water changes? If a pipe bursts they sometimes have to route the water from a different source and the taste changes.
Washing up/dishwasher residue?
Or you've got the rona, in which case hope you get well soon.