Management link does not always work

Since a while i’v upgraded to the ‘reloaded’ version.
Almost everything works great except this:

The [manager_link] in the email does not always work.
8 of 10 thimes it redirect to the right page and the user can magage his subscribtions. 2 of 10 it goes wrong and the user get the same page but is asked to enter his email for sending a management link.

When this mail is received, the link is the same, and still not working.

When I enter this mail adress in admin management it shows up and CAN be managed.

There are no caching or other conflicting plugins and as i said, it works allright most of the time.

What can be the issue here?