If fast startup is enabled, the computer is not fully shutting down, but partially hibernating. What Lansweeper is reporting in the uptime calendar is actually correct. Perhaps we can implement a special uptime calendar state for fast startups in a future release, but I'm not sure when development might be able to look into this.
The uptime calendar uses data which should show what is really going on. It might be that a shutdown actually uses an automatic sleep mode. We've recently noticed this on Windows 8 and 10 operating systems.