my old sgpro is also happened this problem. someone hs found the solution. They set the recovery mode on. When that is lost star, it recover the sgpro, and then it is work. It seems to be not prefect solution, but it is work.
Someone say that is caused by the PHD2 and SGpro timelapse issue. that is SGpro rare bug. Sometime that will be happen, not not always. case by case.