I have had the below Archive.is spinner “Loading” without any progress indication on a couple of URLs the last few months and I think they are tied to having special characters in the URL-to-be-archived.
My usual workaround was to first archive in the Wayback Machine, then archive the resulting URL in Archive.is as it would automatically follow the path up to the original URL,
That of course failed when https://web.archive.org/web/*/vx-underground.org did not want to save in Archive.is: either these would give an eternal spinner on the “Loading” page no matter the browser you were using either the escaped %2A or *:
The Wiert Corner - irregular stream of stuff 