I have noticed that, in Dark Moor, if you destroy the buildings that if the Venom is attacking, it may glitch and cease movement. Due to the fact that MP4 extensions are not permitted, I have placed it in an unlisted video on YouTube, and I hope you give it a brief check. https://youtu.be/ZNMcE2-lKfI
... If you feel like this is spam or the like, feel free to contact me. Video is 51 seconds
What caused the bug was destroying his priority building, first a 'tower' (the kind you put units into) then a stone wall. He refused to move after that.