Just want to report what solved my issue.
Repairing the installation did not really do anything, although it seemed the URL process wasn’t always going that long as before.
A simple deinstall and reinstall did not work and the URL process was still there.
A complete new installation was necessary. That means deinstall, cleaning the registry and everything on C:\ of all AVAST remains before a new installation.
The manual cleaning seems to be not as clean as expected.
Now my startup is quick again.