Problem/Motivation
I have a pre-existing media type called "Hero banner image" has an image source. That source image field has the "Allowed file extensions" set to "png, gif, jpg, jpeg". It already has a number of items that are used throughout the site. I have now added "webp" to the list of allowed file extensions. If I create a new Hero banner image, it works fine with a *.webp image. However, if I edit one of the pre-existing items and remove the current image file (usually a *.jpg) and then replace it with a *.webp version, I get an error message: "Only files with the following extensions are allowed: png gif jpg jpeg."
Steps to reproduce
Create a media type with an "Image" Media source and save. Create a media item using your new media type and add a jpg image and save. You can now click "Manage fields" again for that media type and add "webp" to the list of Allowed file extensions" and save. Now go back and edit your media item and try to remove the jpg image and add a webp.