NextGen Gallery Slideshow First Few Images Repeat

I’ve been working through all the search results for this problem – I can see at least a dozen people have posted something very similar but the posts are closed without solutions.

The problem is that a NextGen slideshow I have created cycles through the first 4 images several times before continuing with the rest of the slideshow. Please could somebody advise how I can fix it?

It seems like quite a common bug so I’m hoping someone can share their solution!