Window frame on diagonal wall is broken

I have an issue, I made a window but its frame is visible only when viewed from the side or above, and it happens only when it's on a diagonal wall (Everything is ok on a non-diagonal wall). The frame goes invisible when viewed from the front or back. It's especially weird, since I made similar ones for medium and tall walls, and these are perfectly fine.

Here are screens:

Here's the file: www.mediafire.com/file/qq3lrzg26z5s7qa/Inner_Frame_J_-_Short.package/file