Relates to: MC-176095 MC-199660 MC-208679 MC-250985 MC-271303
May also relate to: MC-159560
The bug
There is a 2×2 region of pixels in both redstone repeater textures that, under normal circumstances, can never be seen due to always being obscured by a torch element. It can be removed without causing any visual differences (disregarding MC-73186), which should communicate that this area is unused to resource pack creators, and may also reduce the file size.
How to fix
An easy fix - just replace the vanilla block/repeater.png and block/repeater_on.png files with the versions attached, and replace Programmer Art's with the fixed Programmer Art textures as well.
Further notes
As noted in MC-268042 and MC-268057, while this texture change should ideally cause no visual changes, MC-73186's continued existence may cause some incredibly insignificant visual stitching around the bases of each torch. This is a very non-notable side effect, and fixing MC-73186 will get rid of it, meaning that this bug (MC-268056) will cause no visual changes at all upon being fixed.
muzikbike
Can confirm