Hi
Yes it happens because the empty slot fields not saved yet to the database for this you must add all the images to the slider images fields and after that remove the images which you dont want to display for example you have three images in your slider right now so you just add all the seven images once only and after that remove that seven images since you need only three so the default images will remove and customizer saved the blank image= field to the database then you will see only three slider on the front end.
If you still having trouble while doing this please send us the login details with site url to support@flythemes.net we will fix it asap.
Thank You
