[2020] Roof of Canals Exploit?

Just played a map of Canals where the defending team was able to get on top of the crates using Anvils barricade. They were able to access the top of the crates and the roofs of the buildings. At points it looked like they were walking on invisible platforms. It gave them full vertical control of BOTH bomb sites and made attacking into them utterly miserable since there is no hero or path for the attackers to use to get on their level.

Has anyone else run into this exploit? Are there any devs that are willing to share some more insight into whether this is legit or not?