Database inconstistency in nG6
Problem: 673 links project/run while the run doesn't exist anymore. The most recent run in this series was made Monday 3 April 2017 22:00:00. (This error impacts at least the migration process.)
SELECT * FROM
tx_nG6_project_run WHERE run_id NOT IN (SELECT uid FROM tx_nG6_run)
Tests: Deleting the run via the web interface also deletes the link. So the inconstistency doesn't come from here.
Remove the obsolete links
Test if the purge process is responsible. (It shouldn't delete the run nor the link.)
Update the database structure to add an integrity constaint.
Check if the analyzes have the same problem (project/analyze, run/analyze, analyze/result).