Generally the update via GUI is automatically disabled when the docker_manager needs to be updated first.
When you update via GUI the docker_manager you need to run the ./launcher rebuild app command to rebuild your discourse site, but because you have to do that, in this case is more profitable if you upgrade all (docker + plugins) directly via SSH.
For example, I always update from GUI, after finishing the updates I do the docker restart. When I see that the docker_manager want the update I do that via SSH, skipping the update via GUI, because my site goes offline for a few minutes anyway.