Deferred spotlight shadowmapping, weird artifacts.

Been working on implementing simple shadowmaps, but I’ve came across some weird issues. I’ve been at this issue for almost a week now (a few hours here and there) and cant figure it out

This is the relevant shader code:

/* 'viewPosition' is saved in GBuffer and written as ViewMatrix * ModelMatrix * VertexPosition
 * 'linearViewDepth' is saved in GBuffer and written as LinearizeDepth(gl_FragCoord.z, nearclip, farclip)
 * 'uniform_shadowmap' is a texturesampler for the shadow depth map
 * 'uniform_snearclip' and 'uniform_sfarclip' are the near and far clip planes for the shadowmaps projection
 * 'uniform_invViewMatrix' is the inverse of ViewMatrix
 * 'uniform_lightViewProjMatrix' is the viewprojection matrix for the spotlight "camera"
float LinearizeDepth(float depth, float near, float far)
  float z = depth * 2.0 - 1.0;
  return (2.0 * near * far) / (far + near - z * (far - near));
void checkShadow(vec3 viewPosition, float linearViewDepth)

  vec4 worldPosition = uniform_invViewMatrix * vec4(viewPosition, 1);
  vec4 lightPosition = uniform_lightViewProjMatrix * worldPosition; /= lightPosition.w;
  vec2 shadowUV = lightPosition.xy * vec2(0.5) + vec2(0.5);
  float linearShadowDepth = LinearizeDepth(texture(uniform_shadowmap, shadowUV).r, uniform_snearclip, uniform_sfarclip);
  if (linearShadowDepth < linearViewDepth)

More descriptive with annotations, a visible spotlight frustum, and lower shadowmap resolution for clearer results.

Old video:

Any help, tips and/or recommendations are highly appreciated!