In 24w33a the UV for all arrows (and bee stinger) were split into two textures. However, the Programmer Art spectral arrow wasn't changed so now its invisible from some angles.
Steps to reproduce:
Enable the Programmer Art resource pack
Shoot a spectral arrow at a block from above
Move downwards and look at the spectral arrow
Observed result:
The spectral arrow is almost invisible at certain angles.
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Expected result:
The spectral arrow is visible from all angles, like in 1.21.1:
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Can you please provide more information? You can do so by providing the How to reproduce steps, and attaching a video/screenshot showcasing the bug.