The most obvious indication is that of the cabin being roped off, as it’s seen here with a red cord and flag hung across the entrance, preventing guests from stepping in.
Other gondolas, while not roped off, are purposely skipped by Cast Members during the guest loading process due to issues with opening and closure mechanisms. Gondola doors are having problems opening and closing, and remaining closed, with many stuck in the open or closed position.
The door on this and some of the other gondolas do not completely close.
The area of this photo circled in red shows that the doors of the blue gondola also do not completely close: