I am using Office 365 (v2016) for my daily work and to get the latest updates I am in Current Branch.
Today I exprienced the down side of Current Branch - all of a sudden Excel was starting to consume high CPU usage, even when no actual work was done there.
I checked Office version in File - Account - About Excel and noticed that Office version was 16.0.6741.2021.
Google didn't show any issues, so I just upgraded to latest Office 365 version and the issue disappeared.
So go to File - Account - Update Options - Update Now and update.