Apologies, comment didnt post before when i fixed.

The Gloucs/Bristol coastline had separately been changed to a coastline tag. Have changed some coastline/boundary tags back to Administrative Boundary tags to fix the broken loop.

As for the estuary, it was marked as adminstrative boundary connected to the mainland and yeah, appears as a land border. Photo included:
https://i.gyazo.com/9b1df7e426db98c0cf5e70ee36297214.png