Process is executed and closed immediately

I have a long running process with tasks and service calls inside.
The process was always starting & working good.
Now without changing anything I am getting after starting in the response that the process has already ended (ended: true).
Requesting the engine-rest/history/process-instance/{id} shows me that the process was completed and used only ~300msec to run.

PROBLEM SOLVED.

Can you upload the the model and also show me the details of how you started the process?

Thank you for caring. But I solved it was a process internally problem.