Installed Modals-v12.0.0-dev2516548-PRO on Joomla 4.2.6.
Created a Modal Popup with a table as content. Styling is fine after first opening (1). After page refresh, modal background and styling is getting corrupt (2). (using Firefox Browser if it matters)
See:
That is down to the sub-template setting and whatever that file does.
By default Modals will use the 'component.php' sub-template file of your main template.
You can change that, or change the component.php so that the necessary style sheets get loaded.