Pix-Star photo Frame

I am using the TVersity free version until I see if it works OK. I have a Pix-Star Photo frame and using the PS4 as media playback device as advised by Pix-Star but the pictures only show on the frame as thumbnail size. Pix-Star say there might be a setting in the server to adjust the picture sizes? or is it a case of somehow deleting the thumbnails from the Picture folder?

Sometimes however the correct sized pictures do show on the frame ok. So it looks like it is getting the thumbnails from somewhere?

I am using Windows 11