DD2 did the same. She started preschool/DC at 2. Was fine til she was 4 & going 2 days a week.

Then suddenly she just didn't want to go anymore & would cry as soon as she found out it was DC day. I don't know why, coz I know she loved it.

It was getting to the end of her last year before school anyway & we were having money problems, so I pulled her out, but she went to school with not a single issue at all! Still can't get enough.

I'd say its just a phase, but maybe that one extra day is too much? I don't know, I'm thinking about putting DS in for an extra day depending on how our housing situation goes.