Image in parallax section doesn't load

I use on my homepage three times the parallax section with image position „background full“ or „background small“. In this case the background image is not always loading. Only a refresh help to load the background image, but not always. I attached some screenshots.

Here is the link to the homepage:

Thank you for help!

Best regards,

Hello there,

I hope you are doing well today.

Please use the following plugin to clear your browser cache:

Also, please disable your third part plugins to see if one of them may be causing a conflict.

Best Regards,