Unfortunately, FreeRTOS does not provide a single list of all generated tasks. Instead, it manages several lists, depending on the task state. The tasks are rearranged and re-listed when they switch the task state.
If the task list is displayed, while the target is running (aka emulation access or dual-port access), the debugger reads the task lists sequentially. It can easily happen, that the lists are not consistent over this time period, causing the debugger to read broken task lists. This results in a temporary wrong display with a changing task list.
If the target is halted within a task, the lists are consistent and the task list display is correct.