In a shipwreck near my spawn point ( near the ice biome ) there was a minor glitch. When I opened the second chest the game was not responding as it should and after 5 seconds or so teleported me 2 blocks down inside the water and then the chest opened. No hang or game not responding.
EDIT: Maybe generating the treasure map was a reason for this. My mistake not to mention it.
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Coordinates: 461.584 / 59 / 431.482
sounds like MC-126244, but that has been marked as fixed

Can reproduce, the treasure map points to approximately 1242/308, which might be a bit far away and hence causes the lag.
Please run /debug start before opening the chest then run /debug stop and then run /debug report . Please attach the report from the file location %Appdata%\.minecraft\debug
Very similar issue on MC-192229 which was just merged, opening these chests caused a memory error and crashed our server.

In 20w29a.
The closest shipwreck in the seed you provided was not in a cold ocean, please provide the exact coordinates.