I just found a fix:
Go into the settings of your the affected module (in the standard Joomla module list, not pagebuilder) and into advanced settings.
On the bottom, there is an option called "module style" and the already chosen option is "inherited".
Change the option to "html5" and everything should be displayed again.
Note: this is an option I never ever paid attention to in many many Joomla years, so I don´t really know the technical background of this option, it was just a lucky shot. I don´t know if this option could affect your Joomla installation in any (maybe negative?) way.
Can someone of the support team confirm that this is the right way to solve this issue?
Thanks!