The bug
There are few pixels in the illusioner texture that are left behind.
A few blue pixels near the arms and the other is a gray/grey line that is above the torso which it is visible in-game.
In the Programmer Art resource pack, non of these extra pixels are presented.
The issue wasn't completely fixed in 1.18-pre5 as mentioned by @unknown in this comment.
Default (after first fix attempt)
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Default
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Programmer Art
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This wasn't completely fixed, the gray line is still present, except at the top of the model where there were supposed to be empty pixels. The line is still visible in-game at the bottom of the model, has 6 unused pixels on both sides, and the 2 pixels at the top of the model are gray, rather than blue.
Affects 1.19-pre3 too.
Can confirm in 1.19.

1.19.2.

This bug can be fixed with Resource Pack though, still not sure if this will eventually be officially fixed since Illusioner is yet not a formal feature.
Hi there!
I can confirm.