i just declared war against the country(an AI), i checked all the provinces before declaring war, in those that didn't hide troops due to fortress, it had 15 in the city, the moment i declared war and first artys shoot, AI units moved. but this particular unit didn't move like the rest, it teleported way forward
the bug is triggered when moving the units(my units) that are in front of them, towards the city,
here an example: https://i.gyazo.com/6cbb5cc90017165e83dd988980f86702.mp4
here's another example: https://i.gyazo.com/b168edeb2c26fe295390db584421bd3e.mp4