Hi Ondra.
I have problems with old legacy material in my previous scenes, I can see the textures perfectly in viewport like before but when I click render, the textures shows with error and sometimes it show other texture not assigned. Every time I hit render, the textures are different.
Please see attached images:
Viewport.jpg --> Viewport screenshot
Render-1.jpg --> First render
Render-2.jpg --> Second render
Render-3.jpg........
I`ll try to change all textures to physical material to check if this change works.
Best.