Hi,
I defined a simple rule that every week send an email with the list of the open Issues to the Assignee.
The List is filtered for a determinated Project.
Actually we have 12 assignee to open issues in the project, but only 10 of them receive the email correctly.
The rule is as follows:

The Users are correctly confirmed (with the email address)
I added some Log actions to try to debug, but I had no results.
What I can see:
1) The lookup issues block give as result a list with 12 distinct users in the field assignee
2) The first Add value to the audit log lists 10 Email to: strings (separated by ",")
3) The Email has been sent to the 10 users listed in the log, not to the other 2
Some one can help me understand what I'm missing?
Thanks