Arborvitaes tip blight

Most issues homeowners have with arborvitae are due to poorly drained soil or under or overwatering. What you described could be caused by a number of things, including root rot (https://pnwhandbooks.org/plantdisease/host-disease/arborvitae-thuja-occidentalis-root-rot), tip blight (https://pnwhandbooks.org/plantdisease/host-disease/arborvitae-thuja-occidentalis-tip-blight) Cypress Tip Moth (https://pnwhandbooks.org/insect/hort/nursery/hosts-nursery/arborvitae-thuja-cypress-tip-moth-0), or beckermans blight (https://pnwhandbooks.org/plantdisease/host-disease/berckmanns-arborvitae-platycladus-orientalis-berckmanns-blight) among other possibilities.