slack in 2015: "We have no indication that the hackers were able to decrypt stored passwords, as Slack uses a one-way encryption technique called hashing."

slack in 2019: "In 2015, (...) The attackers also inserted code that allowed them to capture plaintext passwords as they were entered by users at the time. "

This reflects poorly on them. Unless they discovered only now that the 2015 hack included capturing plaintext passwords.