Quote: "Just changing the format will not solve your issue, you will need to modify the segment FPS file or the entity FPI file to find the correct image,"
Your theory will not apply here. The pack in question are
entities, using just a jpg texture file. The method of applying a D, D2, will not solve it.
Quote: "just change the textures to png. format it worked for me."
That also works. We actually did that to use in v1.18. I also recall when I placed dynamic lights in the map the buildings disappeared.
Perhaps the OP could shed more light to the map layout- are there dynamic lights? What version of FPSC is being used, etc.

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