Asterisk ODBC MySQL 100% CPU crash

I’m currently facing a very strange behaviour with an Asterisk Installation on a t2.micro EC2 amazon instance.

If I place the sippeers via extconfig over ODBC in my amazon rds mysql database and then place ~50 calls with sipp to an extension asterisk crashes within a short time completly with 100% CPU load. No SIP Registrations possible anymore. No invites possible anymore. I have to restart Asterisk to do Invites and Registrations again.

If I make the same with the same Asterisk machine, but change the MySQL Host, User and Password to an identical local MySQL Server everything works fine even with ~500 calls.