When you remove the app Product Filter & Search, please make sure that you publish another theme without the filter. If you don't have any backup theme, you may get the error popup when browsing the collection page. In order to resolve the issue, please follow these steps:
1/ Install the app again
2/ Go to Filter Setup -> Revert Setup
3/ Select the theme you would like to remove the filter
4/ Click on Remove Filter
If you have any issue, please feel free to let us know (email@example.com), we are happy to help.