It is very likely that you are having issues with the official LinkedIn app (given its reviews and ratings). It has not been updated for almost 2 years. Therefore you might want to try this unofficial LinkedIn app for Windows Phone/Mobile!
This app provides access to a mobile site of LinkedIn, but this mobile site is not accessible via the browser on your phone!
Advanced features (in-app purchase required):
- notifications for new messages, new notifications or new invitations on linkedin.com (shown on live tile)
- sync your lnkd.in contacts to your phone