I guess there is something wrong with the auto save function.
Couple days ago, my GK disappeared, sent manager ID to Lian, got fixed.
Today, I almost lose my GK again, this time it just disappear, leave 10 men on the formation. Luckily, I tap revert button and my formation back to normal.
Both time my GK disappear when I change formation fast,
first time, I even didn't notice my GK disappeared,
this time, after revert back, I change formation slowly and nothing wrong happen.