Error: An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /mySite/en/batch?id=50&op=do Sta

I get this error when I try to Reindex all products at: admin/config/search/search_api/index/product_display/status

An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /BASE/en/batch?id=50&op=do StatusText: Internal Server Error ResponseText:

This happened after I created a new taxonomy which a I added as term reference to the product display and then enabled this field as a Facet.

No error notifications in the logs.