Not sure if this is intentional, as most mobs lose aggro when unable to pathfind to the player but Shulkers seem to become permanently aggressive when struck while open with no possible teleport option until player is over 16 blocks away or switched to creative mode.

Line of sight / time does not reduce aggression through blocks (Glass Panes) when timed against Zombified Piglins. Aggression also persists against player when switched to Peaceful Difficulty while in the above mentioned range.