CI3 Update Multiple Tables

I don't know which v2 you used where $this->db->update('table1, table2'); worked. The signature of the method is the same in v2.1.4 and v3.1.7 and looks like this.

PHP Code:

public function update($table = '', $set = NULL, $where = NULL, $limit = NULL) 


The second argument is an associative array of update values in both.

The only reason I can think of that your "update()" syntax worked is that the "DB_active_record" class had been extended with, for example, a "MY_active_record" class that overrides the "update()" method.