I understand that there might be several different tools outside there and I will have a look in the future.
But please - this post is about a specific problem,...

I will have a look to get something better, but not immediatly
I first try to understand. - I created an extended event session (SQL Server 2014) but I don't...

Oh really ! So what you say is that there is nothing to understand ? And I hope that the fact that it does not work does not mean that...

yes they execute without any problem

Deleted the plan and recreated it - same error
Is there really no way to understand whats happening ?
How can I rebuild the index now ?

Ok thanks for the link !