Tane, if you don't have any users logged in at the moment you have cpu 16% it does not mean there's no processes going on the background, users getting notifcations via e-mail, cron is working every( I don't know how often it is on your server)

What hosting plan do you have?

Do you have any other websites installed on the server?

Yes, I appears to have been something like that. It hasn't dropped below below eight but then it hasn't appeared to have caused any errors either. With four users logged in though, it is sitting on 20% which doesn't seem to bode well. I shall have to wait and see. Is there a plugin that would show the background processes or a logs plugin I can use.

Tane, can you please contact your hosting provider and ask for more details regarding your high CPU, like query logs, which part of the software causes that high CPU etc. 

I would consider this closed if someone wants to close it. Although the site used higher than normal CPU usage after the upgrade, it never reached the limits on the server. I wasn't watchign at the time but after recently upgrading the messaging plugin I believe it settled down even more.

Thank you, Ross.

Ok, thanks for letting us know.