Why would freeRTOS threads which schedule properly on an F4 fail to do so on an F7? One low-priority thread steals the processor and never yields.

[Sking.21]

The running thread runs vTaskDelay() as it did on the F4. It does not help. Adjusting thread priorities has little effect. Other threads (all started with higher priorities) should have plenty of opportunity to run but almost never do. It all ran fine for years on the F4.