The bug
In first person mode, when sneaking while using a fishing rod, the fishing rod's line immediately jumps to the new position of the fishing rod the player is holding, instead of transitioning along with the sneaking animation.
To reproduce
Cast a fishing rod
Sneak
❌ The fishing line "jumps" immediately to its new position, instead of transitioning smoothly.
Video
[media]Linked issues
is duplicated by
relates to
Attachments
Comments
Can confirm for 1.13.1.
Can confirm for 1.14.3 Pre-Release 3
I think this bug exists because the old sneaking from 1.12 and prior used to be only one frame, so it didn't used to be a bug in the past.
Issue is not fixed in Minecraft 1.14.3 pre-4
Also affects swinging animation.

Blocked from testing in 21w11a, by MC-219849
Bug still occurs as of 1.20.4, though I think that was known.
This impacts any camera height alteration animation, not limited to sneaking. It pertains to the camera animation when initiating or halting swimming, gliding, or using riptide too. Relates to MC-269001.
Can confirm for 1.21.4
This is the main bug I wanted fixed. It's such a small issue but bedrock doesn't have it.
Can confirm for 1.13.2.