Figuring out which operation EF is blocking

I get

System.NotSupportedException: Second operation started on this context before the completion of the previous asynchronous operation. using "wait" to ensure that all asynchronous operations have completed before calling another method in this context. Any member of the instance is not guaranteed to be thread safe.

Get it completely, I know how to solve it in theory, which is not a problem. But for the life of me I can't seem to find a valid operation calling the block.

This is in production, at medium loads. I cannot reproduce it while debugging. So I need to throw information about pending EF requests in some way.

Thank!