If a unit with an insignia set by BIS_fnc_setUnitInsignia/Arsenal changes uniforms mid-mission to a uniform without an "insignia" hiddenSelection, players who join the mission after the uniform switch will see the insignia's texture forcibly applied onto one of the unit's model's hiddenSelections.
This cannot be fixed by calling BIS_fnc_setUnitInsignia with an empty insignia, as the command will fail due to the uniform not having an "insignia" hiddenSelection.
Seems to be fixed temporarily by reequipping or changing uniforms, but players who JIP after this'll see the glitched texture again.
Bug has been around for at least a year, if that helps.
Happens with both player and AI units.
All testing done with v7 performance binaries on version 2.00 of Arma 3, but can be reproduced with stable branch.
Screenshot when uniform has "insignia" selection: https://imgur.com/a/D8uLKfe
When uniform is changed to one without, but without backing to lobby: https://imgur.com/a/KJsN5cH
After backing to lobby and rejoining: https://imgur.com/a/TUP7wLn
After reequipping uniform, looks exactly like Screenshot#2
Update: this is actually caused by switching to any uniform where index of insignia in hiddenSelections array is different from original uniform.