This behavior was introduced in 21w16a.
The bug
The position that the game draws the fishing line changes depending on what aspect ratio the game is being played in. The correct behavior only occurs with a window size that has an aspect ratio of approximately 16:9.
The issue occurs no matter what FOV is set. The attached screenshots were taken at an FOV of 80.
Steps to reproduce
1. Use a fishing rod to throw a fishing line.
2. Change the horizontal size of the game window.
3. Notice how the fishing line's location disconnects from the fishing rod.
Observed behavior
The fishing line will be rendered offset to the left of the fishing rod when playing with an aspect ratio with a lower width (such as 4:3) and to the right of the fishing rod when playing with an aspect ratio with a higher width (such as 21:9). The offset direction will be reversed when the fishing rod is held in the left hand.
Expected behavior
The fishing line would take the aspect ratio into account when determining its position on the screen.
This duplicates MC-6579