My PC has never rebooted or required a reboot following a Sonos update. Sounds very odd. 

It could be related to user rights. The WDCR installer also wants to update the Sonos HTTP service. 

Strangely enough this does not happen on my laptop only my main rig. I do not mind rebooting, but I do mind that it just reboots at end of update without confirming with me, so that I loose my work.

Sonos just don’t require reboots of PCs on update.  They just don’t.  That is why there is no warning.  If it has been triggered by the update then it is a rare, unncessary and unintended consequence, not a deliberate part of the process.   There must be some setting on your PC that is causing this unusual response to a Sonos update.  At the moment, @ratty ‘s speculation is the only show in town.

Just checked my event viewer. MsiInstaller starts the update, It then calls the RestartManager which fails, because Kaspersky Anti-Virus-Service could not be closed. Next it reports SonosLibraryService failed to start. MsiInstaller then registeres a reboot is needed and then it just reboots without asking.

During next update I will try and disable Kaspersky to see if that makes a difference.

The “Service cannot be started. The handle is invalid” message from SonosLibraryService is perfectly normal, assuming there are no files being shared from the PC to Sonos.