Thanks for the help guys...
- @DaveM121 The 3rd party app I'm using is called WindowBlinds but I've been using it for 10 years or more and it never caused this problem before. I tried "Pin to Start" which then shows the app as pinned but still leaves it at the LHS.
- @Anonymous A couple of weeks ago I installed a trial copy of Norton 360 antivirus and to be fair that coincided with this issue happening (timewise) but uninstalling Norton 360 hasn't helped.