After upgrading to Wave 5.0 you will need to connect your system via Wave Sync as the upgrade will disconnect the Wave Sync account from the Wave system. However connecting after the upgrade may not work, unless you disconnect from the Server, Client, Wave Sync portal and apps.
On the client, disconnect from Wave Sync here: 
Then check the account is unsynched on the Server: 
Log in
And disconnect here: 
Then log into the Wave Sync web portal
Ensure the account is disconnected there
Finally disconnect from the server in any apps and restart the Wave services and reconnect the Wave Sync account to your system