Widget Importer & Exporter plugin not working
Did you receive an error when importing your widgets that says "you must upload a .wie file generated by this plugin"? WordPress 5.0 introduced a change that can prevent .wie files from uploading on certain sites.
Here is an easy workaround: install and activate the Disable Real MIME Check plugin. Having this plugin active will allow you to upload the widgets .wie file. You can remove the plugin after you've uploaded your widgets.