While I have had no personal experience with the Mosquito, what I heard was it does not live up to the quality of the Sig Sauer name. For whatever reason many people have/had problems with it. I own other Sig's but not that one. I picked up a walther P22 for my kids to practice with. It is too small for my hands but I see that Sig started making .22 conversion kits for some of its other models.
I would try to get them to fix it for you and hopefully the bugs get worked out.