Just a quick heads up, if you haven't seen the message in your Office 365 message center already take a look. I have copied some of the details below:
Project Online client requirements are changing
Beginning in February, 2017, Project Online will require the latest version of Project to connect to Office 365. We are making architectural changes to features in Project Online which impact older versions of Project, connecting to Project Online.
How does this affect me?
If you are using Project 2016, there will be no impact to the user experience when connecting to Project Online. If you are using any prior version of Project, you will encounter issues connecting to Project Online. This change will not affect you if you are not connecting to Project Online.
What do I need to do to prepare for this change?
Upgrade to Project 2016, by February 2017, to continue connecting to Project Online without interruption. Please click Additional Information to read more about the system requirements.