Linux guest additions use 0.06 Hz refresh rate for custom display resolutions

[refi64]

This can be reliably be reproduced on any Linux guest:

• Install the guest additions onto a Linux guest (tested with Debian & Fedora guests).
• Make sure the package corresponding to the xf86-video-vmware driver is removed, so that the driver doesn't add the resolutions before VBoxClient itself can (see notes below for more details). (On Debian & derivatives, this can be done via sudo dpkg -r --force-depends xserver-xorg-video-vmware.)
• Make sure you've rebooted after doing the above.
• Resize the VBox guest window.
• Run xrandr.
• Observe that any new resolutions added by the guest additions (ending in _vbox) all have a refresh rate of 0.06 Hz:

$ xrandr
Screen 0: minimum 320 x 200, current 1900 x 1920, maximum 8192 x 8192
Virtual-1 connected primary 1900x1920+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   preferred     60.00 +
   2560x1600     59.99  
   1920x1440     60.00  
[...]
   1024x768      60.00  
   800x600       60.32  
   640x480       59.94  
   1990x1920_vbox   0.06  
   1860x1920_vbox   0.06  
   1940x1920_vbox   0.06  
   1900x1920_vbox   0.06*
[...]

This completely breaks the ability to use recent versions of Electron applications w/o xf86-video-vmware, which seem to respect this refresh rate when rendering.

Notes:

• This doesn't occur if xf86-video-vmware is installed because then VBox doesn't add the new resolutions itself: since both VBox & VMware use SVGA, xf86-video-vmware picks up the resize first and adds the resolutions it wants, after which the VBoxClient --smsvga sees a matching resolution is already present and does nothing.
• This has been reproduced on multiple different host systems.

[refi64]

Log file, including resizing the guest

[galitsyn]

Thank you for reporting the issue. It should be fixed in VirtualBox 6.1.36. Please refer to https://www.virtualbox.org/wiki/Downloads page.