SQLite error and tasks stuck

Hello everyone,

Currently I am experiencing huge problems when scanning targets.
I have a distributed OpenVAS setup, meaning I have one management instance and several distributed scanner machines.
Since about two weeks, every time a tasks gets started, the tasks seems to be stuck at 1%. From time to time, a single tasks jumps to ~80% out of nowhere, but this is rather an exception.

When observing the openvasmd.log file, I get a lot of the following error warnings:
md manage:WARNING:2018-09-07 05h02.11 utc:25512: sql_exec_internal: sqlite3_step failed: interrupted
md manage:WARNING:2018-09-07 05h02.11 utc:25512: sqlv: sql_exec_internal failed

I am running OpenVAS on a Ubuntu 16.04 server.

Many thanks in advance for any ideas or solutions.

Best regards,
laughing_man