I'm seeing this exception when trying to load .xlsx attachments.
I turned on ignore errors to false and I see this error now when loading .xlsx files.
{"error":
{"root_cause":[
{"type":"mapper_parsing_exception","reason":"Failed to extract [-1] characters of text for [null] :
Could not initialize class org.apache.poi.POIXMLProperties"}],
"type":"mapper_parsing_exception","reason":"Failed to extract [-1] characters of text for [null] :
Could not initialize class org.apache.poi.POIXMLProperties","caused_by":{"type":"no_class_def_found_error","reason":"Could not initialize class org.apache.poi.POIXMLProperties"}},
"status":400}