Flag-transitive block designs and unitary groups (vol 193, pg 535, 2020)

In this note, we cover a gap in the proof of [2, Proposition 4.3]. In conclusion, Theorem 1.1 in [2] is revisited: if D is a 2-design with gcd(r, lambda) = 1 and G is a flag-transitive almost simple automorphism group of D whose socle is PSU (n, q) with (n, q) not equal (3, 2), then D belongs to one of the three infinite families of Hermitian unitals, WittBose-Shrikhande spaces and 2-designs with parameters (q(3) + 1, q, q-1), or it is isomorphic to a design with parameters (6, 3, 2), (7, 3, 1), (8, 4, 3), (10, 6, 5), (11, 5, 2) or (28, 7, 2).