Thank you @kautuk_sahni in my case the ui.assetfinder.js is located in the cq-ui-wcm-editor-content.1.1.500 package. The reason they differed on the different environments was that the SP install had not completed successfully. Re-installing the SP on all environments resolved the issue.  

Hello all, I have two AEM 6.5 environments both with SP 6.5.20 installed. However, the file at /libs/cq/gui/components/authoring/editors/clientlibs/core/js/ui/ui.assetFinder.js differs between the environments and this is causing issues. I need to understand where this file came from so I can align ...