My macOS install got into a state before the Christmas holiday where something would spawn #corecount amount of process. They seemed to be related to processing

My macOS install got into a state before the Christmas holiday where something would spawn #corecount amount of process. They seemed to be related to processing thumbnails for contents of directories. This would go on for a few minutes in which the machine was completely unresponsive including the mouse. So it seems possible still to bring a high core count machine to its knees. But something then is indeed very wrong.