I just noticed that a new BIOS version 1.0.9 was posted today August 27. The driver details page on the website notes this for fixes and enhancements with this release:

Fixes:
- Fixed the issue where the external monitor displays a distorted Dell logo when you turn on the system with the lid closed.

Enhancements:
- Supports Realtek RTL8153DD-CG Ethernet Interface Controller.
- Improved the system stability.

https://www.dell.com/support/home/en-uk/drivers/driversdetails?driverid=h4f5t&oscode=wt64a&productcode=xps-13-9305-laptop 

My 9305 has BIOS 1.0.8 released in May. I haven't experienced the issue with the external monitor. For enhancements I don't use an Ethernet connection only wifi. If I knew what was behind 'Improved the system stability', that would be helpful!

Is it worth updating the BIOS?