Hi,
Your problem is caused by Bookeo plugin, I turned it off and now the background slider is showing normally.
I check your website and see you have many similar plugins installed, please note:
– With the cache plugin, use only one cache plugin to compress css, html and cache, not using too many different plugins, this leads to inefficient input conflicts.
– We support BA Booking plugin for this theme, so it is not necessary to use other similar booking plugins, which can also lead to conflicts between different plugins.