I've been doing a lot of work with a client on Jet Reports recently. While we were doing a training session, we created some new users and changed some from being ordinary users to being designers via the Jet Licensing portal. When the first user launched Excel, they found they were still an ordinary user without access to design mode.
They logged out and back in without the license changing at all.
The key to resolving this, was for that user to reactivate Jet Reports using the Activate from Jet Service Tier option on the Jet ribbon to to pick up the changed license.