The cause of this sudden quirk? Adam, a user on StackExchange, came up with a way to test what was happening and fully documented his results.
The result? The machine would slow down while the fans on the device went into high gear. On StackExchange and other sites, MacBook Pro users documented situations where charging using the left side USB-C ports caused unusually high CPU usage. While these powerful notebooks have USB-C / Thunderbolt 3 ports on both sides, we’re going to tell you why you should charge your MacBook Pro using the ports on the right side. Photo via hardware Do you have a recent MacBook Pro?
Right-side USB-C ports on a 16-inch MacBook Pro.