I'm a long-time lurker and have created an account specifically to post on this thread.
I lost my two 7 month old kittens at the end of May, within a week of each other. Reading the OP and messages on the FB group, it sounds horribly familiar.
My kittens suddenly became anaemic, with low white blood cell count and v low white platelets. I noticed sudden loss of appetite, refusing to eat or drink, lethargy, temperature and, in the case of my first kitten, some diarrhea.They were referred to a specialist for treatment (my second kitten in particular was referred v early because I was obsessively monitoring for any sign of her becoming unwell), but they were unable to save them. My second kitten became ill 5-6 days after losing her brother and it followed a very similar pattern.
The specialist vet has said they don't have a confirmed cause but they are investigating what appears to be "a new development of disease in the cat population" and I understand they are working with the Royal Veterinary College etc.
I was feeding them on Applaws Dry Kitten as well as Felix AGAIL Kitten wet. I still have the bag of Applaws, have just checked and it's the same batch number listed by Chihuahuacat. I'd be absolutely heartbroken regardless, but the idea that I may have inadvertently fed my beautiful little kittens poisoned food just makes me feel sick to my stomach.