Two-sided is enabled and it does not happen on a plane, it happens on meshes with faces that overlap for example a box which makes it show the plane underneath the one im looking at
Does anyone know what is causing this and how I can solve this?
Another option you could try is to brute force it using sorted translucency. In the actor settings there should be a sort triangles option:
You can try enabling that on your mesh with the translucent material. It may be unreliable though, and sorting is per-triangle so you may still get some overlap
In addition to these options, there is also a project level setting to enable “Order Independent Transparency” in newer versions. This is much more reliable at solving sorting issues, but it will make all translucent materials more expensive. Maybe not a big deal if your goal is arch vis, but for real time use it’s much better practice to:
not use transparency at all.
not let transparent triangles overlap.
keep their size in screen to a minimum.
Not only does this cause the aforementioned sorting issues, but it also causes overdraw, as the background, and multiple layers of the expensive translucent material need to be rendered on the same pixel multiple times, significantly increasing the time needed to draw those pixels.