Thanks for keeping this thread updated.
To provide some more insight to what the problem was for anyone else who is interested – if your WordPress destination address (can be your domain or your IP address) or blog ID changes , then your GrabPress Autoposter (backend) connector will break. Autoposter needs to know your domain or IP to send posts or messages from our remote server to your server – once this changes, your connection breaks.
It would be great if we could send an error message to the plugin to let users know why their Autoposter connector has broken, but unfortunately, without the connector, there is no way for us to communicate with our backend. The best way to prevent this from happening is to use a DNS or domain name when you install GrabPress, as opposed to an IP address (that may change, depending on your service provider).