To know what's recently been imported, navigate to the Ingestions page.
The ingestions are listed in reverse-chronological order. Use the search form at the top of the page to filter the list. Clicking on the ingestion ID will provide more information regarding the respective ingestion.
The following image is an example of an ingestion that failed. Note the ingested count vs the failed count. For more information about the failed records, download the log file.
The log file contains a row for each failed record. The last 3 columns have details regarding the error: original_line_number, error_message, and error_backtrace. The error_message column will be most helpful. The error_backtrace column is for internal purposes.