Between versions 1.14.3 pre1 and 1.14.3 pre2 mouse reacts a lot more sensitive. Either in a fresh 1.14.3 pre2 world or converted from pre1.
I only noticed when upgrading to 1.14.3 since I usually only play full releases. Then I did some tests and found the issue to be occuring since 1.14.3 pre2.
More people reported this when 1.14.3 launched:
https://www.reddit.com/r/Minecraft/comments/c4pjj8/minecraft_java_edition_1143/
https://www.reddit.com/r/Minecraft/comments/c5bmbv/sensitivity_change_in_1143/
https://www.reddit.com/r/Minecraft/comments/c4qgbh/experiencing_mouse_sensitivity_issues_on_java/
Might be related to lwjgl, see https://bugs.mojang.com/browse/MC-144107
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violine1101
Duplicate of MC-155147
migrated
That's not a simple increasement of sensibility... I noticed a different speed on X axis and Y axis... seems that moving the view top-down is slower than left-right. So it's very bad play in this status.
(sorry for my english, I'm not native speaker)
Noticed this immediately upon updating. Had to reduce my sensitivity to 70% but it honestly feels like a different acceleration curve of some kind