What I figured out, yet:

This blog runs by subdomain.
But the URL for resetting the passwod mixes up both: subdomain and base_url (e.g. https://tourismus.genba.org and https://www.genba.org/blogs/ …)

The link, sent to reset password was:
https://tourismus.genba.org/blogs/htsrv/login.php?action
instead of
https://fokus.genba.org/htsrv/login.php?action (which works)

@saunders What is the $baseurl of your site?

@fplanque $baseurl = 'https://www.genba.org/blogs/';

@saunders can you please also confirm that https://www.genba.org/blogs/htsrv/login.php?action works?

@fplanque yes, this works.

@saunders can you please screenshot how your collection urls are configured in the back Office?

Especially this panel: http://b2evolution.net/man/assets-url-cdn-settings

Here it is:

Hello @saunders, I could reproduce the bug with following configuration:

• $baseurl = 'http://b2evo.yb/blogs/'; is used as URL of Home collection (this domain is linked to path like /www/b2evo/, but the b2evolution root is located in the folder blogs/ really)
• URL of Blog A = http://sub.b2evo.yb/ (this domain is linked to path like /www/b2evo/blogs/)

A wrong URL is http://sub.b2evo.yb/blogs/htsrv/ when we requested a password reset from Blog A.
When a request from Home collection a result was correct http://b2evo.yb/blogs/htsrv/ as expected.
After my fix in commit https://github.com/b2evolution/b2evolution/commit/06b0f804fef5704a2d4e19b23949aa1ee88fff81 the URL is correct for Blog A = http://sub.b2evo.yb/htsrv/ and for Home = http://b2evo.yb/blogs/htsrv/.
So currently it must works as expected, please check this, thanks.

@yurabakhtin Great! That fix works pretty fine and solved the problem! Thanks! Awesome support