I sometimes notice this weird behavior of arty not shooting after being given an attack order.
If you set unit to move in circles, then arty just follows it. Sometimes zthuee fires, i have seen lobo do it too, but meduza\fervor almost never do it and only run .
But those units "will" shoot if stationary.
TLDR: something brakes then fast unit run in circles(gets in & out of weapon range) vs t1 artillery.
Example:
https://www.awesomescreenshot.com/video/5855085?key=64e52f7e8b5b6cd4985bf84ba37ec389