The Discussions module is a module that was discontinued in 4.11 after the 4.10 update turned it into Conversations. It is still possible to use the module on islands if you had it before the update.
Typically, when you have this island on a page, there is an Add New Topic button in the top bar, and a column at the end for deleting Topics. If you do not see these, the culprit is the page is a public page. The island itself doesn't check to see if you are accessing it through the public page before removing those two options. If the page is public at all, no matter how you get there, the options will be missing.
The solution to fixing the issue is to make the page not a public page.