Normally healthy cats with runny stools

I have 3 cats, two of them have runny stools. Their appetites re healthy normal and they are alert and frisky. Just in case I switched their crunchy to Medical crunchie from the vet. Should I be worried?

IT is NOT normal for cats to have runny stools///

What were they eating >>??? and which Medical is it now and did THE VET put them on it ...

I was feeding them royal canin and yesterday changed to MediCal, a brand only sold at vet's offices. I'm trying to isolate which one has the stomache upset. Both are healthy, playful, eating and bright eyed. Both had a little cream the other day ( a friend left her dessert plate unattended) but not a significant amount, maybe a few licks. Jessie is 11 and terrified of vets. She poops when I put her in the carrycage.

Suddan food changes ARE likely to cause digestive issues.. especially in a "senior cat"

if you can name or link the two foods it maybe easier to figure out any BIG issue ingrediants

Royal Canin Intense Hairball mixed with Royal Canin Light 27. They started on 11th September and were okay until 18th. Then the runny stools start.