We have the following series of breakers and subpanels

Mains - 200A Main breaker - 200A Subpanel with 200A breaker
-- 100A Subpanel with 100A breaker -- 30A Subpanel (but no 30A breaker)

The 30A Subpanel consists of 6 20A breakers that connect directly (via
the busses) to the 30A incoming line.

Now there is a 30A breaker on the 100A Subpanel but *no* 30A breaker
on the final 30A subpanel. The 30A subpanel is located across the
house from the other panels which are all located in the basement.

Is there any problem with not having (another) 30A breaker in the 30A
subpanel itself?

Thanks