Yes, it is illegal and has been due to the bracers dropping out of the prep. The “and remain stationary” wasn’t added in to keep them from dropping down. It was added in because we realized we had that in all other braced releases but not on flips. It wasn’t really an issue when you had to have two bracers, but we could see them trying to move while flipping. This is illegal because during part of the flip, the bracers are no longer in double based preps. I would look at wording like below.
Illegal under rule 3-3-5. While the new braced flip rule allows a single hand/arm connection for the braced flip, the rule still requires that the bracers are in double based preps with spotters during the skill. In this video, the bracers are lowered out of the prep position while the top person is flipping. Bracers must be in the double based prep when the flip initiates and until it is caught in order for them to be in a position to provide the proper support. They don’t have to wait until they are fully in the cradle, but clear contact must be made prior to moving out of the prep position.