MODx "$rs not set! New variable not saved!" Error

After upgrading MySQL on a new server I noticed an issue with MODx not being able to add Template Variables. I managed to find a workaround by setting the sort order to "0" which allowed the new Template Variable (TV) to be saved. The problem wasn't solved though as the TV would not store any content. The solution was to change the MySQL configuration to remove "STRICT_ALL_TABLES" or "STRICT_TRANS_TABLES" from the "sql-mode" in the MySQL ini file.