stockpiled material in the last quarter of 2020

As did many others. Stockpiling is a great way of buying time while the problems are sorted, and with luck they get sorted out in time to restore a normal flow before the stockpile runs out. But is it far from certain.

That may be why haven't had too many supply problems yet. If the problems are sorted, we won't either. But if they are not, the issues will really start to bite once the stockpiles are used up.