Scan operation waits

Whenever i start scanning, no row is displayed and the scanner get Screenshot from 2017-12-18 17:42:13stuck at 50% or so. never resumes.

It does not “hang” because if it hung, you won’t see progress bar at all. It WAITS. Waits for backfill that apparently does not arrive. Check your data source, turn off “wait for backfill”, retry.
It looks like unsupported third-party data source being used.