Maybe it’s just me, but lately I have had troubles with my engineers freezing up when I am trying to build rally points. He wacks his hammer two or three times then stops with his hammer in the air, so I move him, and again, wacks it a few times and stops. Sometimes if I keep going eventually he will build it, but lately it is taking so long to build anything that he’s getting killed before he can ever finish. Maybe after almost three years, I’ve lost my touch. 
He doesn’t have that problem if I build an ammo crate or anything else.