We recently made a gym switch in order to compete JO rather than Xcel. We would have loved to stay at the old gym if DD was selected for JO there -- Old gym is a top/high scoring gym, with super JO coaches, beautiful facilities and a super convenient location. DD had lovely Xcel teammates, and I really liked the other parents. On the negative side, I had serious issues with the gym's philosophy re: exclusivity and selection for JO, and felt they mishandled that process with respect to my then-6 year old DD (who received a JO offer that was rescinded 3 weeks later with little explanation except that DD was maybe too old or too tall or both). Also, Xcel is clearly the "step-child" of the gym with significantly fewer hours and less experienced coaches. In any event, I was very careful to handle the switch in a positive and respectful manner, so the door (Xcel door) remained open.
We are a couple of months into the switch, and the new gym is not perfect. Much longer commute, less supportive teammates, somewhat harsher coaching style, and lower scores (albeit with a much larger and more inclusive JO program). However, we knew most of this going into the switch. And, if you ask my DD, she is still glad for the change. She can compete JO, is making progress, and seems to be getting better training/coaching/hours than if she had stayed in Xcel at old gym. So for now, the pros outweigh the cons.
Not sure this qualifies as a "negative story" -- I guess we will find out more once competition seasons starts -- but I certainly agree with those who say that gym changes are almost always filled with pros and cons.