I know you said you threaded it correctly, but did you threaded it in the correct order?
Seriously, this was my problem for years! I was either just threading them in any random order or just left to right (I forget) but it was wrong. If you can't get a fix for it, I would take it back to the place you had it serviced and explain that it's not worked right since then and can they thread it and test it. Maybe they'll catch something you're missing, or maybe something went wrong with the servicing and they'll make good on it.