Messages from the scanner (openvas is the name of the scanner component only) have nothing to do with the behavior of the gvm-tools. You need to look at the gvmd.log file to see some output.
GMP is a request/response protocol just like HTTP. The connection is closed if an error happens. Until an error occurs you might issue several commands over the connection. But it has never been used for a stable long term connection and it seems this isn’t working well with the authentication. Therefore I would strongly suggest to re-create the connection for long term queries.
To get all results in one response for a report you need to use the ignore_pagination=1 filter keyword like here