interesting bug, sorry for the trouble! you're advertising your webmention endpoint on some of your URLs, eg https://abisso.org/stream/2020/11/03/e-ora-che-sono-dentro-e-tocca-a-me-lo-spid-di-siel/ , but not others, eg https://abisso.org/59VC3V . bridgy caches webmention endpoints by domain, and it sends wms in a deterministic order, so it tries https://abisso.org/59VC3V first, sees that it has no endpoint, caches that, and skips the other one. you can work around this in the short term by advertising your endpoint on all of your posts. not ideal if you deliberately chose not to, though, i know. bridgy's caching webmention endpoints by domain isn't ideal either - details in #601 - but it has to do webmention endpoint discovery on hundreds of thousands of URLs per day, so it's a tradeoff.

Yes, #1 should fix this. And Bridgy follows redirects when it serves wms, but not rel=canonical or anything else, so it will probably send the wms to your shortlinks. (I'd recommend setting up redirects anyway, we generally find that serving content on shortlinks instead of redirecting causes problems like this over time, but up to you!)