Unsupported mime type: image/gif - Sudden gif upload error

Hello, Kirby3 user here (3.5.1). Something rather strange happened to our website when it suddenly started rejecting gif uploads (this was not a problem beforehand).

Previous pages with gifs seem to be working, one can even duplicate them and replace the gifs. However I cannot create a new page and upload a gif as thumbnail anymore. When I try to do so, I get the error message “Unsupported mime type: image/gif”. The blueprint for the page is as follows:

title: Default
  listed: true

    - Large

  - width: 1/1
        label: Info
        type: info
  - width: 2/3
    # This column only has a single field
        label: Preview Text
        type: writer
        label: Inside Text
        type: blocks
  - width: 1/3
    # This column only has a single field
        label: Date
        type: date
        required: true
        width: 1/4
        label: Tags
        type: tags
        width: 3/4
          - People
          - Papers
          - Prototypes
        label: Author
        type: users
        label: Thumbnail
        type: files
        multiple: false
        max: 1
        template: Thumbnail
        width: 1/6
        uploads: images

I have already deleted the media files, cleared site cache and added accept and mime statements without success. Could you please help me out? Thanks, B.

What is the content of this images files blueprint? Does it have an accept property and what is set for this prop?

The blueprint for images is:

title: images

  mime: image/jpeg, image/png, image/gif, image/svg

Just to verify: This issue happened out of nowhere? You didn’t make any changes at all to your website or changed the Kirby version etc, right?

If that is true, then I assume that your hosting provider changed something resulting in mime type rejection.

We have made changes to the website, but not to the blueprints themselves or to the individual pages. As far as I know, the Kirby version also stayed the same.

What you could do is test if it works locally (assuming that the error happens on your production server).

Also, is there any stack trace to this error, i.e. where it originates? Or is there any more information in the server and php error logs?