Since the 1.16 Nether update went live bubble columns no longer work in flowing water. For example, in my Minecraft Realm we had several 1x1 columns for mob farms and for elevators from bedrock to the surface that stopped functioning after the update. Source blocks that are uninterrupted from the Soul Sand will produce bubble columns but any flowing water above the Soul Sand cuts off the bubbles.

Here's a Reddit thread related to the topic where other users are experiencing the same:
https://www.reddit.com/r/Minecraft/comments/hesetu/bubble_column_mechanics_changed_in_116/