E-Mail sending via CRM results in -> POST https://xxxxxxx/index.php 500 (Internal Server Error) / csrf-magic.js:53 (Error)

Dear Vtiger-Team,

i'm trying the "master" repo and when i try to send an email via crm to an email address in the account, i get the following error: POST https://xxxxxxx/index.php 500 (Internal Server Error) / csrf-magic.js:53 (Error)

i can see the error, when i open the browser debugging. Mailserver is successfully configured and i get the notification email.

Account and Contact creation is working as expected without errors.

Does anyone have an idea?

Best regards Ralph