Hello,
Could you please try to increase Load delay time in “Load delay” property of your lightbox web part or control?
Load delay time (in milliseconds). If you are using automatic resizing, this value indicates how long will be lightbox wait for taking element size. If you have problem with displaying of lightbox content, try use upper value.
Please also try to store files in File system (
Where the files are stored) for better performance and also please use Generate thumbnails option:
Files related settings I would also highly recommend you to try to decrease the size of images (the resulution or increase the compress ratio).
Best regards,
Helena Grulichova