There was actually a very obvious reason for the toilet paper shortage during the first lock down.
Every day, millions of people use the bathroom at work, or at restaurants and bars, or at public facilities, or at the homes of their family or friends.
Suddenly, people were doing 100% of their bathroom business at home, which caused a huge disruption in the normal market distribution of toilet paper.
Not to mention, a lot of people found themselves suddenly stuck having to eat their own cooking!