problem in porto theme in refreshing home page

hi
i installed porto theme the latest version. and install one of demo. but my problem is when some one for first time visite the site, theme is ok and not have any problem. but when you refresh the page it has problem. between slider and below section It comes into being white space. and again when you clear cache in browser it fixed but by refresh it again happen. rugbazaar.ir you can test it. i try it by different browser and systems but it’s exist. my plugins have not problem but theme problem is exist. sorry for bad english!
thanks for your help!

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