Thanks to all who weighed in on this. It appears to be an odd bug with the way Dorico interacts with iStat Menus, the app I use to display system information in my menu bar. When I quit Dorico, the graphs displayed show that my memory usage never goes up over 25% in each of the 24-hour, 7-day, and 30-day graphs, but when Dorico is running, that information is displayed as going up to 100% usage. And yes, the graphs are displaying information about memory usage, not CPU. It’s an odd one, alright. In audition to this post, I’ll report it to the developer of iStatMenus.