Not to mention when there are Russian units wearing Ukrainian uniforms or dressed as civilians.
I'm sure most of these episodes of friendly fire. The most experienced Ukrainian soldiers are in the east. Kiev is mainly manned by drafted soldiers. In a stressful situation when bullets are flying past you, logic can go out the window.
In WW2 there were multiple warnings about German soldiers who had infiltrated behind enemy lines. American soldiers often encountered "German" soldiers in American uniform speaking perfect English speaking to them, most often at night. In most cases it turned to be friendly fire with very little evidence of infiltration.
There was a lot of denial when it comes to friendly fire, because no one wants to be responsible for killing your own and you don't want to hear that your son died because of a mistake.