This is purely up to Qubes. Qubes VM Manager (QVMM) is developed by Qubes. Default DispVM is a Qubes dom0 setting.
Could you please check if Qubes has related issues about this yet?
If not, I recommend to make an argument that is unspecific to Whonix (a general Qubes issues). This increases chances that this bug isn’t confused as a Qubes-Whonix issue and stalling. That this might be specifically important in case of Qubes-Whonix could be mentioned at the end of the ticket.