These issues have all been corrected in 0.5.2 and 0.5.3. The notification is only displayed if the Amazon website is completely loaded, this can take some time because of asynchronous requests. It might happen that you habe switched the tab in the meanwhile.
Note that the blocking is working correctly because the URL is intercepted before the browser even makes the request to Amazon's servers.

If you have further issues, please open a GitHub issue here: https://github.com/timbru31/amazon-tag-remover/issues