Beacons which are created underwater and have 11 blocks of water over them don't give you the "bring home the beacon" advancement no matter what. If there is 10 or less water blocks over the beacon it will give you the achievement. I tested this issue both on 1.15.2 and the newest snapshot and both of the versions didn't give me the advancements. I have provided screenshots of the issue down below.
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Accidentally changed the gamemode category to creative and took it back, sorry about that. The issue first happened to me on survival where I'm collecting most of the achievements. I don't think that this is intended because of the fact that the beacon can still give you effects.
Duplicate of MC-153385
Oh! This is a nice bug report!