GLSL shader uniform locations can't be found

I'm working on a vertex skinning shader, and for some reason my program can't find the uniform locations.

Vertex shader code:

#version 330

const int MAX_JOINTS = 30;
const int MAX_WEIGHTS = 3;

in vec3 position;
in vec2 textureCoords;
in vec3 normal;
in ivec3 boneIndices;
in vec3 weights;

out vec4 fragPos;
out vec3 n;
out vec2 texCoords;
out vec4 mcolor;


uniform mat4 modelMatrix;
uniform mat4 projectionMatrix;
uniform mat4 viewMatrix;
uniform mat4 normalMatrix;

uniform mat4[MAX_JOINTS] boneTransforms;


void main() {



vec4 totalLocalPos = vec4(0.0);
vec4 totalNormal = vec4(0.0);

for(int i = 0; i < 3; i++){
    mat4 boneTransform = boneTransforms[boneIndices[i]];
    vec4 posePosition = boneTransform * vec4(position, 1);
    totalLocalPos += posePosition * weights[i];

    vec4 worldNormal = boneTransform * vec4(normal, 1);
    totalNormal += worldNormal * weights[i];
}
texCoords = textureCoords;

fragPos = modelMatrix * vec4(position,1);

n = totalNormal.xyz;


gl_Position = projectionMatrix * viewMatrix * modelMatrix * totalLocalPos;
}

The boneTransforms uniform doesn't seem to be set correctly; if I query the active uniforms with

GLint uniforms;
    glGetProgramiv(shaderProgramID, GL_ACTIVE_UNIFORMS, &uniforms);
    for (int i = 0; i < uniforms; i++){
        int name_len = -1, num = -1;
        GLenum type = GL_ZERO;
        char name[100];
        glGetActiveUniform(shaderProgramID, GLuint(i), sizeof(name) - 1,
            &name_len, &num, &type, name);
        name[name_len] = 0;

    }

i always get zero; However, if I just put gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(position,1) I get the expected result (correct rendering without any vertex skinning), so the other transforms appear to be working despite it telling me they don't exist? EDIT: this is sometimes the case, other times I get the model at position (0,0,0) but otherwise rendered correctly with this.

I have read about the compiler stripping unused/inactive uniforms, but if I use boneTransforms to calculate totalLocalPos and use that for gl_Positions the uniform should be active.

I try to set the uniform with

vector<glm::mat4> boneTransforms = model.getBoneTransforms();
int location = glGetUniformLocation(shaderProgramID, "boneTransforms");
glUniformMatrix4fv(location, boneTransforms.size(), false, (GLfloat*)&boneTransforms);

location is always -1. Is there something wrong with how I try to set this particular uniform, or is the mistake in the shader code?

EDIT2: I just noticed that the behaviour of my shader changes when I add or remove objects (which use a different shader) from the scene. I don't know what to make of that.
EDIT3: If I remove all other meshes from my scene the shader crashes with an access violation. As long as one other object is being rendered there are currently no crashes.
another EDIT: Apparently accessing the weights variable crashes my shader.