Cannot access Theme Customizer | WordPress.org

Hi!
When I try to access the theme customizer it returns an unloaded blank page.
When checking the logs only one line is printed:

PHP Fatal error:  implode(): Cannot use output buffering in output buffering display handlers in <root-directory>/wp-content/plugins/smart-slider-3/Nextend/Framework/WordPress/AssetInjector.php on line 124

WordPress: 6.4.2
Smart Slider 3: 3.5.1.21
Astra: 4.6.3

 

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