I am unable to reset my password on https://backdropcms.org/ .
I first received the mentioned Error in sending a password recovery email there, then went here to this forum subdomain and tried the same here several times, and then suddently it worked. But only after several tries with the same error as on the main site.
I tried also in guest browser windows with no extensions or the like, but the same problem there.
Now I have recovered my login here in the forum site, but I am still unable to reset my password on the main site.
(PS. I also experienced this last year on the main site, without taking the time to report it. As it still is the same situation now, I report it here.)