FreeRTOSplus TCP STM32F4 Integration

This is because you are calling interrupt safe FreeRTOS API functions from ISRs that have logical priority higher than configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY. One reason for that assert should be the following lines in your code:

/* ETH interrupt Init */
HAL_NVIC_SetPriority(ETH_IRQn, 0, 0);

Which means ethernet interrupts are run at the highest priority.

Try lowering it to configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY or something logically lower (numerically higher).

For example:

HAL_NVIC_SetPriority(ETH_IRQn, 5, 0);