Apologizes. We got it working by reverting to an older version of the Co-Authers plugin. The problem is apparently deeper than we first realized and actually appears to be an issue with the core WP_Query “where” filter, which does affect data queried by Ajax Load More but would also affect anything / everything else using WP_Query, which would include simple template loops and more. Specifically, the problem is that some string substitution appears to mangle the SQL query string, inserting a separate where clause directly into the middle of a table name in another clause.