This is not a duplicate of MCPE-32731 but related. That ticket resolved an issue in which converted drowned were dropping tridents when not equipped with them. I assume that logic has been fixed.
However, I haven't seen in any release notes that the chance of a converted drowned being equipped with a trident has changed. It used to be 15%.
Thank you for your report!
However, this issue is Working as Intended.
The report you have submitted is working as intended: See MC-128702.
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