Hello!
Got this issue when did unwrapping of arch. How to solve it? I tried to delete everything form geometry? leaving only this face to unwrap but nothing changed.
Quick answer, because you are using two or three faces. Difficult to explain. Add more seams or create your own faces WITH THREE or FOUR vertices.
In your example the faces are overlapping, because one or more faces are consisting of more then 4 vertices. Which causes this problem.
Actual, because two of the edges of a single face are overlapping.
The vertex is drawn over to the other side, crossing edges and creating the mysterious faces.
To solve this, build your own faces with 3 or 4 vertices.
Red face A. has multiple vertices, more than 3 - 4. Green the same. Break faces up into smaller ones.
Thank you. Broke in to smaller 4vertex faces and all is fine now. But the odd is that in video curse i follow and did everything as tutor, he didn’t have such problem.