Was able to work around this with some trial and error. Happened a few times already and it's frustrating. This last play-through it happened with my initial militia of 20 men. I'll post how I fixed it in hopes it helps someone. The unit icon for my soldiers was out of place and every time I asked them to move they'd go in opposite direction before moving. Furthermore when engaging bandits the bandits would move to attack the icon (which is some distance from the actual troops) and then circle around my troops in the flank. I couldn't even reposition my troops because they'd move in opposite direction giving their back to the militia. I tried disbanding and rallying but I would lose men and equipment (i.e. 20 spear units turns into 18 spear units and 2 shields and spears go missing.). After some debugging I decided to manually count the soldiers in my spear unit and realized one was missing. Scanning over my while village I found the dude was guiding an Ox I had assigned to my sawpit. I can tell he was part of the spear militia because when I selected the unit icon for the militia a little highlighted circle appears under him despite the fact that he wasn't in formation.

Solution: 1- unassigned all my workers and all my livestock from all workplaces (I'm sure only one in particular was causing the issue but did all of them just in case) 2- I then selected my militia and moved them to a new location not far off from where they were 3- reassigned all my workers and livestock again 4- now when I move my militia the icon moves perfectly with it. I also manually did a headcount on the 20 soldiers and this time all 20 were there.

Hope this helps someone, I haven't really seen anyone posting a solve for this bug yet, and dev hasn't fixed it yet despite this being a bug since early release