Mixing Instanced vs Non-Instanced data in OpenGL - c++

Question

I'm having some difficulty mixing instanced data with non-instanced data.
What I have is an array of GLfloats and an array of GLuints.
The GLuints is my index-data for rendering Elements. My GLfloats is the vertex, texel and depth information.
What I'm doing is collecting all the data required for rendering a series of quads and them submitting them all at once:
For each Quad there are:
Four vertices:
2 floats for the vertex position
2 floats for the texel position
One depth float
6 indices submitted to the index buffer
They are in that order. So after one blit of a texture that I want to show all of it to the extents of the screen I would expect to see (stretch the whole texture to fit screen) (top-right, bottom-right, bottom-left, top-left) (texture coords may seem flipped but they're correct):
Float Buffer
[ 1 | -1 | 1 | 0 ] [ 1 | 1 | 1 | 1 ] [ -1 | 1 | 0 | 1 ] [ -1 | -1 | 0 | 0 ] [ 0.9 ]
[ pos | tex ] [ pos | tex ] [ pos | tex ] [ pos | tex ] [depth]
Uint Buffer
[ 0 | 1 | 3 | 3 | 1 | 2 ]
In case it's not clear, each of the four vertices for a quad are to use the same depth value in their frags.
And so, I setup the buffers like so:
uint32_t maxNum = 32; // this is the max amount I can submit
glGenBuffers(1, &m_vbo); // to store my vertex positions, texels and depth
glBindBuffer(GL_ARRAY_BUFFER, m_vbo);
glBufferData(GL_ARRAY_BUFFER, 17 * maxNum, nullptr, GL_DYNAMIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glGenBuffers(1, &m_indicesBuffer); // to store the indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_indicesBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * maxNum, nullptr, GL_DYNAMIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glGenVertexArrays(1, &m_vertexArrayObject);
glBindVertexArray(m_vertexArrayObject);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glEnableVertexAttribArray(2);
glBindBuffer(GL_ARRAY_BUFFER, m_vbo);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 17, 0);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 17, (void*)(sizeof(GLfloat)*2));
glVertexAttribPointer(2, 1, GL_FLOAT, GL_FALSE, 17, (void*)(sizeof(GLfloat)*16));
glVertexAttribDivisor(0,0);
glVertexAttribDivisor(1,0);
glVertexAttribDivisor(2,4);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_indicesBuffer);
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
And populating the buffers and drawing is like so. The vertexAndTexelData and indicesData are the GLfloat and GLuint buffers discussed above. numSubmitted is how many I'm actually drawing.
glBindTexture(GL_TEXTURE_2D, texture);
glBindBuffer(GL_ARRAY_BUFFER, m_vbo);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(GLfloat) * vertexAndTexelData.size(), vertexAndTexelData.data());
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_indicesBuffer);
glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(GLuint) * indicesData.size(), indicesData.data());
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glBindVertexArray(m_vertexArrayObject);
glDrawElementsInstanced(GL_TRIANGLES,indicesData.size(),GL_UNSIGNED_INT,(const void*)0,numSubmitted);
glBindVertexArray(0);
When I draw all this, I'm getting a black screen. If I take out the depth data and the instanced drawing stuff, everything works perfectly fine. So I'm guessing it's to do with the instanced drawing.
If I put this through RenderDoc I see the following:
Buffer Bindings
So I can see my three vertex attributes appear to be set correctly.
Vertex Attribute Formats
So these appear to be in the right layout and the correct data types.
Mesh Output
However, if I look at the Mesh data being submitted...
Something is clearly wrong. The Depth values all appear to be correct, so it appears the instanced drawing is working there.
But obviously the positions and texels are busted. Interestingly, where there isn't a garbage value, i.e. a -1, 0 or 1, it is correct for that position.
I suspect it's the stride or offset or something... but I can't see the issue.