Blurry thumb slider

Hi Team, I am currently having an issue with thumb sliders in storyline 360. It seems that no matter what the quality or size of image is that I import, when I use the 'picture' option for a thumb when creating a slider, the image used goes blurry, to the point where it is unusable (in the image I have attached, there is a standard slider at the bottom and a red arrow pointing to the image used as a thumb).

I have made sure I have imported it at full quality, the thumb is expanded to fit the height of the track and storyline is up to date (I have also tried using the fix of setting the image to 'visited' - and every other option from all the threads related to this). I would appreciate your help with this as it is currently blocking a project I am working on.