5000 crawl-errors through non-excisting concatenated link

After changing my website from “normal-html” to wordpress, and 301 redirects by htaccess from old urls to new urls, i get a strange 5000+ crawl-errors at google webmasters program, caused by non-excisting links coming from non-excisting pages like https://www.kirtan.nu/agenda.html/contact/mandukya/fotos/int/fotos/de/de/namen/muziek.html

I did some research and screaming frogg says the page https://kirtan.nu/agenda.html redirects 301 to https://www.kirtan.nu/kirtan-agenda-de-zingende-ziel/, wich is correct. Then it says https://www.kirtan.nu/kirtan-agenda-de-zingende-ziel/ redirects 301 to https://www.kirtan.nu/kirtan-agenda-de-zingende-ziel/

1 I don’t know where that second redirect comes from. How can I find the source of this?
2 can this cause a redirect-chain?

any other suggestions what to do?

gr
HAns