Do you experience problems during downloading?
Check your connection in Status and Interface settings window.
Use Test Server in Config > Servers.
We will probably ask you to do a test using only basic settings.
Do you experience problems during repair or unpacking?
Enable +Debug logging in the Status and Interface settings window and share the relevant parts of the log here using [ code ] sections.
How about the SAB reference download:
In SABnzbd's upper right corner, click on the wrench symbol ("Status and interface options"), then click on first tab Status, and click Test Download 1GB. How does that