@sheik_azar git URLs are not a valid way to install Cesium for Unity. It uses native code, which will be missing when installed that way. Instead, you need to use our scoped registry or the built .tgz file, as mentioned in the top most. The Quickstart has detailed instructions for using the scoped registry.
Hi @Icekettle, welcome to the community!
Now, when I run my old game program, it works normally. What could be the reason for this?
You could just be getting lucky. The problem won’t appear until certain problematic tiles are downloaded. Of course, if you’re not using Google Photorealistic 3D Tiles at all, then you shouldn’t have any problem.
Another possibility is that Google has fixed this! We have been in contact with them and have been informed that they are working on a fix on their end.