As for the plugins, this is community work, you may get more information from the authors.
What do you mean with this?
There have been cases where a shutdown, for some reason, takes up to a minute or so after indexing a library.
Try it again, reboot and see whether it is consistent.
What is confusing is that after turning off Volumio via Android client, the spinning Volumio icon does not stop. But as far as I can judge, the client is probably shutting down. Anyhow, the UX is not top notch.