What could cause Inaccuracies in a Tippmann A5?

I have had my Tippmann A5 for little more than a year now, but it has been less accurate the last month. I did have an accident with it two months back, but a technician cleared it 'in working order'. I promptly replaced the damaged parts, with identical ones, and it went back to normal, until about a month ago. It has a straight-line barrel, a response trigger and an air through -stock. I run HPA, not CO2, because it is supposed to be more reliable. What could cause this issue?