Troubles with fixed element on layout

Good morning,

we have integrated the plugin on a site we are developing and will need to integrate it on other sites in the near future.
The plugin is really complete and well done; however, we are experiencing a problem and can't solve it.
Our layout necessarily requires some DOM elements to have a fixed position. As soon as we initialize the plugin, from the browser the elements lose their original positioning, although the inspector css is correctly read.
Can you tell us what causes this problem?
Thank you very much.