We had one of our plugins on Create of Opportunity however during the import of the Opportunity record it was not working properly. We had the Depth check in our plugin code to check for infinite loop as the same plugin was being used for Update also.
After some debugging we realized that Depth value is 2 instead of 1 during import.
To test this, we created a sample plugin for create of Test entity record and then imported the Test entity records.
As expected the import failed and we got our custom exception in it.
Hope this helps..
