As @Aherys said, make sure you save all first, and make sure the error you get when building includes Assertion failed: StreamingTextures.Num() == StreamingTextureGuids.Num(), otherwise it’s likely a different error.
If it is that error, try running the plugin, saving all, and restarting the editor. Run the plugin again and let me know if it still is saying it’s changing ids. If so that likely means it’s trying to change the GUID of something it can’t edit. If that’s the case, please let me know, and I should be able to make an edit to the plugin to account for that.
Also, if possible, open up the output log after running the plugin and let me know the name of the textures that it reports have changed.