Sweet Bay leaves browning
You did not mention seeing any insects, but browning leaves may be caused by the bay sucker. If you see any small scaled insects, especially on the undersides of the leaves, they are bay suckers. The first signs are of leaves curling around the margins, and then parts of the leaves turn yellow and then brown and fall off. The best treatment is to keep an eye out, which you have done already, and remove the insects by hand. If a few leaves are badly affected, prune them off. Then spray the undersides of the leaves with a very diluted washing liquid solution. Keep the plant from drying out. Good luck.