Critical error every time I clear JS/CSS cache

@mediaj first, my apologies for this late reply! There’s likely a PHP error there and we need to get the actual PHP error message generated in the background. You likely received an email as WordPress sends one whenever this particular message about the critical error is shown. Please setup and install the “Error Log Monitor” plugin and try to clear the caching again. That error should nicely show up within the Dashboard’s widget.

PS: There were changes made to the plugin lately and it’s very likely the problem has been solved as I recall there were some issues with the scandir() function used on non-existent directories. Please use the development version for testing which has the latest updates. Here’s how to get it: https://assetcleanup.com/docs/how-to-get-the-development-version-of-asset-cleanup/