What cause a PCB track to break
Unreliable traces are usually a problem with the PCB itself, not caused by soldering.
So, review your PCB production data (Gerber files) and make sure the copper of that traces continues under the ring of the via. Look at the ring of a board that's not soldered with a strong magnification (microscope?) to see whether there's anything suspicious. Also, look at the whole trace, not just the ring. If that't the case, contact the company that prints your PCBs, and explain the situation.
I really don't see any other reason the trace would break if it was not badly executed by the PCB factory.