Image size reduced

When adding images to an existing slideshow I could not get de slider to use the full size good quality images. I can not find any setting that controls the image size that is used.
Until now I never had this problem… What has changed? Can I set the quality somewhere?

Now Gutenslider uses the large-image size set in ‘media’. I did a workaround by setting the large image size(media setting) to 2048 an uploading the images at 3840 – then the 2048 images are used.