We've got an email studio audience that we want to do a decision split on after sending an email (with a 7 day wait between). We're making the decision based on the entry DE, but whatever filter we create we get an Invalid Expression error.
It turns out the error disappears if you save your journey.
I get this every time I edit the attribute group in data designer i.e unlink the DE referenced in the decision split. Have you checked there yet?