40x errors are cached in an exponential back-off manner. If the transformed image is accessed before the original is loaded, the system returns 40x and this returned 40x error is cached, first for 1 minute, and the cache period doubles every time until settling on a maximum 24-hour cache period. If you upload the original after the transformed image is cached, you need to wait for the cache to expire for the transformed image to appear, or use a different transformation.
Note that if the error has reached the 24 hours caching period, accessing the transformed image before the original was uploaded would result in the error being cached for another period of 24 hours.
Other transformed images that were first accessed after the original was uploaded will work as expected. In other words, please make sure the original image is fully uploaded to your Cloudinary account before attempting to access any of its transformed image's URLs.