Hello again! After seeing your post, Haru, I updated the skill.c file to the current commit. The auto attacks no longer trigger the --- failed assertion --- error. However, Magnum Break does. Maybe more, I haven't tried other skills yet. Funny enough the error only triggers if magnum break hits things. I used magnum break with nothing around me for fun, then when it hit targets later it triggered:
[Error]: --- failed assertion ----------------
[Error]: c:rotrunksrcmapskill.c:179: 'skill_lv > 0 in function 'unknown'
[Error]: --- end failed assertion -----------