CfgTaskTypes that are defined in the description.ext are not shown when creating a task. The problem lies in BIS_fnc_setTaskLocal. The script does not look in the missionConfigFile (only the configFile). The documentation states the TaskTypes defined in the mission and in the configFile will work (however, this is not the case)
https://community.bistudio.com/wiki/Arma_3_Task_Enhancements#Visualization {F27272}