Projectiles will only despawn like arrows when they hit a block thus if you get a lot of arrows inside a bubble column, you can create server/client lag or even crashes down the road.

While I understand this change could be controversial due to some players liking the ender pearl machines but this has to be fixed at least if there is a lot of them due to the number of lookups the entities do and can be exploited on servers and has been on 1.14.4.