Im having the excact same problem. Im using a forticlient vpn which gives me a unique ip adress. As the op Im also trying to use the synchronization feature. Im trying to replicate the folders from the local machine onto a remote server. Whenever I reconnect from the vpn connection it tells me to manually type in the ftp password even tho Ive enabled the possibility to automate this.
Please start a new topic for your problem. There, describe how did you "enabled the possibility to automate this" and include a full log file.