Issues with integrated server.
It randomly hangs while client keeps running. Easy way to spot it blocks stop dropping. This can last for several seconds to minutes.
Its so bad integrated server hangs on every save world event and closing game with world saving can take more then 5 minutes to resume activity.
Could not test with external server if issue happens there too, my Linux server has not fresh enough openjavadk to run it available.
On that note, 1.16.5 with several mods and 1.17.1 runs just fine.
Thank you for your report!
However, this issue is Invalid.
Performance drops are expected to happen between versions, especially in snapshots. Simply stating that "My game is laggier" is not helpful for Mojang to diagnose your issue. If you can pinpoint a specific cause when lag happens for you, please open a new report for that specific issue. If you think this might be a hardware issue please contact Community Support as they might be able to help with your issue.
Keep in mind that Mojang is constantly optimizing the game and simply playing the game provides feedback to Mojang on which parts cause performance issues. To learn more about this, head here (section "Telemetry") for more information.
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