My browser / operating system: Windows NT 10.0, Chrome 64.0.3282.140, No Flash version detected
Several backgrounds and costumes have been replaced with grey squares with question marks upon exporting the project.

Are you using Microsoft Edge as your browser? I suggest trying using another browser and seeing if you have the issue there - I've heard that Edge has some incompatibility issues with Scratch.

CatsUnited wrote:

Are you using Microsoft Edge as your browser? I suggest trying using another browser and seeing if you have the issue there - I've heard that Edge has some incompatibility issues with Scratch.

I have, but im using windows 10S which doesn't allow you to run chrome and my computer wont let me switch out of S mode.