the system check reports all green and I have updated to the latest version (3.9.1).
But the problem persists:
Every time I create a report which includes a graph, the email is not sent, but only when I selected "german" on my profile.
No error is reported.
When I disable the graphs via "Display tables only (no graphs)" OR selecting English as language, all is working fine.
Just tried it and was not able to reproduce the error.