Hill's Science Plan Light Mature Adult 7+ Chicken - cat wet food

I bought the Hill's senior light for my 11 yrs old, slightly overweight tom.. Otherwise very healthy,the poor mite suffered persistent diarrhoea for about 2 weeks whilst eating the dodgy product, even though i have been very careful in introducing the new kibblets on a slow, gradual basis as usually recommended for a change of diet. Indeed he has lost some weight whilst on it but I'd rather he got slimmer without his guts being damaged, obviously..

My cat (tonkinese) can't tolerate these kibbles. They give him severe diarrhoea. I tried twice at different times and these kibbles are definitely a problem. Is there a manufacturing issue? My cat has never had this kind of problem in 13 years.