The mobile sharing functionality is quite limited at this time, this is because of the way android share works, currently if you share from chrome (mobile) all Joplin receives is the url. It is possible to get the name of the sharing page, but it would require the Joplin app to download the page, so the functionality is a long way off.
I have the same problem when I want to share an article from browser or a RSS reader app. Probably the Android has some type of API for handling this kind of share.
When I share a page from Chrome app or gReader pro, the GMail or SimpleNote app handles the title and the link well.
But when I share from the SimpleNote app to Joplin, everything is fine - probably the Android has (least) two kind of share mode.
I can handle it, that I share first to the SimpleNote app, and I after I share from SimpleNote to Joplin - but it could be fine, that I can share url directly to the Joplin app