I don't know if it is some kind of bug but I would like to let you know:
When I try to connect to the CORE SFTP Server SOMETIMES the connection is unexpetedly closed by the server (SFTP protocol). My workaround is to reconnect until the connection is stable
Sometimes it is neccessarray to reconnect several times (3-5 times). If the connection is stable, everything is working fine (e.g. until reaching idle timeout)...I've recognized that the frequency of "bad connctions" are higher, when I manually disconnect and then try to reconnect only a few seconds later...