Hey Sylvia, this looks weird! Could you send the custom block model file to support@kenney.nl so I can check the issue and possibly fix it? Thanks!
I can replicate it with your city building blocks. It's definitely not a visual bug, we lose parts of the model when importing them.
Hm? I don't understand what's going on in this example. Do note that we don't support version 1.3 of Asset Forge anymore since we solved numerous bugs in the 2.0 release that'll be soon ported over to MacOS/Linux.
