The bug-
When Minecraft is placed in a water-logged Minecart rail, when player is standing right beside it the Minecart Disappears.
How to recreate-
1. Get a Minecraft, rail, some block (preferred to be transparent) and water in a bucket.
2. place surrounding blocks and put water inside of it.
3.place your rail inside the water to turn it water-logged.
4.place you minecart and push it to the edge of the block.
5. start walking on top of the transparent block and see when you'll get close to it the minecart disappears.
6.if you want you can use the new lightning rod block chain on any other block that acts the same to see that the Minecart will disappear only in the water-logged area.
7.I have uploaded a video of how to do that on reddit https://www.reddit.com/r/Minecraft/comments/l1rwl4/i_think_i_found_a_minecart_bag_in_the_new_snapshot/?utm_source=share&utm_medium=web2x&context=3
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duplicates
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Avoma
This appears to be a duplicate of MC-197328, which hasn't yet been resolved. If you have any additional information to provide regarding this issue, feel free to comment on the parent ticket. If you feel that this issue is affecting you, feel free to vote for the duplicated ticket, to give Mojang a basic idea of how many people are impacted by the problem. Just to further inform you, this will not determine how quickly the bug gets handled or fixed.