When a mob converts to another mob, it loses all of its scores.
Exactly same issue as MC-270842 but it doesn't seem to have been fixed properly in this snapshot. (24w36a)
/scoreboard objectives add test dummy
/scoreboard objectives setdisplay sidebar test
/execute summon zombie run scoreboard players set @s test 1
Run the commands above and then convert the zombie to a drowned. You will notice that the score in the sidebar disappears.
/give @s water_bucket
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Can confirm:
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