virtualbox.org

Host: Debian Jessie 8.5. Video is Nvidia GeForce GT730, driver 340.96-1, with Nouveau drivers blacklisted.
Guest: WIN 10 Insider Preview, Build 14946
VirtualBox 5.1.6, 256Mb Video Memory, 2D +3D acceleration enabled, 4 cores out of 8, 4096Mb base memory.

Guest system was stable and screen was clear and flicker free with 3D Acceleration not activated in setup until I was required to check that box in order to install Insider Preview 14931. With 3D not activated, 14931 would not install. However, activating 3D has resulted in strong screen flicker within running apps and occasional over all screen flashing. Within news apps, the story will suddenly go blank (all white) and will not re-write the screen until arrow is centered over news story and mouse wheel is turned. Same occurs when preparing test documents using LibreOffice for WIN and Thunderbird.

First attempts to solve resulting screen flicker / flashing issues by rolling back driver compatibility to WIN 8 and WIN 7 resulted in a conflict between VirtualBox video driver and Skype, causing the latter to crash and terminate. I have experienced this conflict in a number of installations of various versions of VirtualBox and WIN 10 over the past 1+ year that I have been a Windows Insider member. (The problem was much more pronounced in the later 4.x versions of VirtualBox and the pre-v.1515 versions of WIN 10 Insider.) A subsequent installation of a later Insider Preview, without any change or update to VirtualBox, solved the conflict. However, screen flicker and flashing have returned. I tried installing VirtualBox Guest Additions in Safe Mode, trying compatibility settings off and set to WIN 8 as well as with compatibility switched off. Neither produced appreciable change. Likewise, installing as Admin doesn't help, either.

I have not yet tried other fixes recommended for earlier versions of both VirtualBox or WIN 10. Looking for advice on current workarounds.

We need to see a VM log. With the VM fully shut down, right click it in GUI. Select "Show Log" and save "VBox.log" (ONLY) to a zip file. Attach the zip here.

File added.

Try reducing the number of cores to two. You have an AMD "8 core", which actually means a 4 core plus the AMD equivalent of hyperthreading (two threads per core).

Beyond that, I think your problem is with the graphics drivers on your host. Plus, the fact that you're running a beta version guest OS.

Thank you for your suggestions. The change changes the nature of the flickering -- from flickering individual horizontal refresh lines to whole icons and pictures, but the rate at which they flicker appears to have slowed. Reducing the video memory (something suggested in a Microsoft Forums discussion when the recent major changes began to appear circa Build 14915) does not cause any appreciable change.

Acknowledging that this is a discussion group for Windows Guests, I'd like to ask you to expand on your comments re: Debian video drivers. Anything specific and / or can you refer me to any discussion of native Nvidia drivers in another section of the forums? Installing and using Nouveau drivers is not an option on this system. They do to Debian Hosts what VBox drivers do to WIN Guests.

No, I don't have any specific knowledge of your Debian drivers - I don't use Debian or any other Linux host - but bad Linux drivers or GUI package is a regular problem around here, plus the fact that Linux is not the main focus of the graphics card maker.