This can be a problem since ocean ruins are one of the only reliable way to find a horde of drowned zombies, and drowned zombies should be holding treasure so that you can collect the treasure by fighting off the drowns. To reproduce, just explore some ruins with the gamerule doMobSpawning set to false to see what I mean.

Code analysis

OceanRuinPieces.Piece.handleDataMarker(string, pos, world, random, box) does not call EntityLiving.onInitialSpawn(difficultyInstance, entityLivingData, nbtTagCompound) when spawning a drowned.