Error when exporting CSV batch (PHP 7.1)
Per https://civicrm.stackexchange.com/questions/26895/cant-view-exported-batches-datatables-warning
TLDR; PHP 7.1 crashes when exporting CSV batches due to an issue with undeclared array subdimensions.
PR is here: https://github.com/civicrm/civicrm-core/pull/12946