Zombies that have been converted to drowned through a water column no longer drop tridents, gold ingots, rotten flesh, or nautilus shells. I began to notice this after I updated my bedrock dedicated server to Minecraft version 1.10. When using my drowned farm that drops zombies into water columns to convert them for farming gold, tridents, and xp that they didn't drop anything but the armor they had on.

I thought it might have been a fluke so I continued to farm the converted drowned until I had harvested around 1000 and there were still no drops other than the armor.

After this I went to a creative world I use to test ideas out and I spawned 200 zombies into a water filled room for conversion and then farmed them. Again, there was no gold ingots, rotten flesh, tridents, or shells. 

Next, I spawned 200 drowned with a spawn egg and then farmed them. To my surprise they dropped all of the regular drops for a drowned. It seems like the problem is only effecting zombies that are being converted to drowned, and not drowned that might spawn naturally in an ocean or river.

I would really appreciate it if this was fixed. I use my drowned farm for multiple different reasons and resources and I have put a lot of time into it.