Hi tatooin, I think the problem is similar to mine (Openvas with PostgresSQL Could not authenticate to manager daemon)
I have quite 700 Tasks and 20 daily scans (during the night).
In the beginning i used SQLite3 and had the connection problems with quite 300 tasks. The problem was SQLite timeout and I solved modifying the openvas source code.
Because this is not a good idea, I tried to use PostgresSQL but today I have the same problems.
I think the problem is still about timeout connection to the DB.
I create a my own (simple) interface in PHP end connect directly to openvas PostgresSQL and it works, so the problem shouldn’t be the DB.
Hope this helps.
Giovanni