I had a similar issue with this with the developer module...what I had to do was deactivate, uninstall and delete module, then redownload and install to get it to work properly.  It looks like the discussions module is still on 9.01, whereas rest of modules that need to be updated are already 10.x.  I do understand though that deleting and completely removing a module such as discussions would not be beneficial especially in an established site.  But as a last resort, that's what I ended up doing.