Re #6371. Lower logging level for monitor check.

The live stream doesn't have monitors, so we don't want to
normally see this log message over and over.
Re #6371. Add a test for the last change to this algorithm.

Confirmed that without the fix, this test would fail.
Re #6371. Remove temp file that I added mistakenly some months ago.
Re #6371. Improve some error messages.
Re #6371. Some protection against an empty log.
Merge branch 'feature/6371_step_scan_gui' into develop