On IE both display correctly each time the page loads, but the lower slider has a large amount of white space underneath it.
On other browsers the lower slider does not display the images, only the navigation circles.
Refreshing the page fixes both issues.
I have reduced the image size so there is not undue load on the page but can not think of / find any other solutions.
I can’t see any of sliders on provided page on first load. Only navigation panels of slider are showing on Chrome browser.
There are some erros in browser console (press F12 to view it) from your website theme: http://prntscr.com/k4884c
Errors in JS can cause such kind of an issue, because they stop loading of other scripts on a page.
So most likely there is a conflict with your other plugin or your theme. We hope you understand that we can’t test our products with all other plugins and themes that are available on the market, and we can’t control the other developers. Therefore bad code of other plugins or templates can provoke a lot of problems.
Please try to deactivate all your plugins one by one and check the issue. Thus you will find out which plugin causes the error. If it won’t help, try to switch temporarily to a standard WordPress theme.
More useful information you can find here: https://supsystic.com/tips-for-solving-issues-faster/
Afterwards let us know about the result. This will help our developers to solve your problem faster.