Fatal error on Export in 5.18.1
Yes I think you're right. This one seems to be an issue with the combination of "Merge All Contacts with the Same Address" and using Selected Fields instead of primary fields.

I'll put up another ticket: https://lab.civicrm.org/dev/core/issues/1302

Fix looks like it will be in 5.18.2
https://github.com/civicrm/civicrm-core/pull/15452