Currently, Microsoft has published this guidance
Scenario: Users report slow performance when using the system. One issue could be a blocking statement. Blocking by itself is typical in a healthy system and is only a problem when it becomes excessive or starts degrading business activities.
That last point is a big "sort your self out statement". The reality is it takes some digging and we found the most helpful area now you understood the statement is to go to the performance metrics. This query should be poorly performing and should show in this area. If you have any concerns this could be custom code please get your dev team to review the indexes and best practice information around performance. Outside of that sometimes an execution plan run by Microsoft is not always best so we have before request via support detail of the execution plan being used for the query as we may have to insert our own through lcs to stop the issue.
We have also found that the indexing routines used by MS sometimes are not robust enough so as part of the above steps make sure you understand the state of the indexes used by the process that is blocking.
If you've found this thread useful, dive deeper into User Group community content by role