Why does Polyhedron render well on its own but not in combination with complete model - rendering

Question

The code below is an attempt to make a simple 3d triangle to work as side supports for a larger model.
It works well on its own, but when i add it to a larger model, one of the sides of the triangle does not render and I am getting warnings of "UI-WARNING: Object may not be a valid 2-manifold and may need repair!"
To make it even stranger, when I click "save", the model is redrawn and the model shows up complete with the missing side.
I am using OpenScad v.2019.05
I am working around the problem by making a few small objects and hull() around them. I would prefer this code to work, however.
//For some odd reason, this module works well on its own.
//It does does not render correctly when used as part of a larger model.
//Then it will miss a side.
//It shows correctly up when saving though.
module supportTriangle(height=10, length=10, thickness=10){
trianglePoints = [
[ 0, 0, 0 ],
[ thickness, 0, 0 ],
[ 0, 0, height ],
[ thickness, 0, height],
[ 0, length, 0],
[ thickness, length, 0]];
triangleFaces = [
[ 0, 1, 5, 4 ],
[ 0, 1, 3, 2 ],
[ 2, 3, 5, 4 ],
[ 0, 4, 2 ],
[ 1, 3, 5 ]];
polyhedron(trianglePoints, triangleFaces);
}
I am getting warnings of "UI-WARNING: Object may not be a valid 2-manifold and may need repair!" when rendering in combination with larger model

Answer 1

try this:
module supportTriangle(height=10, length=10, thickness=10){
trianglePoints = [
[ 0, 0, 0 ],
[ thickness, 0, 0 ],
[ 0, 0, height ],
[ thickness, 0, height],
[ 0, length, 0],
[ thickness, length, 0]];
triangleFaces = [
[ 0, 1, 5, 4 ],
[ 2,3,1,0], // i reversed these to keep them clockwise
[ 4,5,3,2 ], // i reversed these to keep them clockwise
[ 0, 4, 2 ],
[ 1, 3, 5 ]];
polyhedron(trianglePoints, triangleFaces);
}
supportTriangle(10,10,10);
cube(5,center=true); // just an extra thing to make it error if order is wrong
see:
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#polyhedron
All faces must have points ordered in the same direction . OpenSCAD prefers clockwise when looking at each face from outside inwards. The back is viewed from the back, the bottom from the bottom, etc..