My mullions move closer to one another when the player gets closer. I have no clue why this is happening because they are butted up against the glass on both sides, no seams. Thought it would be fixed by grouping all of them together but they still split.
This is caused by the refraction of your glass. True refraction is not yet possible in real time, so Unreal fakes it by taking the rendered image and displacing it in 2d, thus causing your frames to appear through the glass. To fix it, set the refraction in your material to 1, for thin panes of glass this is actually what you want. Alternatively you could increase the Refraction Depth Bias (it’s in the properties of the material node), but that will probably cause more artifacts.
As above it is refraction causing that issue.
In the material, you can alter the value of Refraction Depth Bias to change the depth at which the refraction starts altering the world. You might get more artefacts at the edge of the glass however, but it’s worth a try. (Click the Advanced Drop-Down Arrow in the ‘Material’ property-heading to find it).