Bug#991417: simple-cdd generated iso: No kernel modules were found

[Mike Depot <mdepot@comcast.net>]

Package: installation-reports

Boot method: "simple-cdd --qemu-only"
Image version: 5.10.0-7-amd64
Date: 2021-07-22

Machine: qemu kvm, on top of bullseye amd64
Processor: QEMU Virtual CPU version 2.5+ (over i7-6920HQ physical)
Memory: 4G in QEMU (64G physical)

I've been using simple-cdd running on my bullseye host to generate a custom iso (also bullseye).  My simple-cdd config had been working fine until a couple days ago.  Now I am getting an error early in debian-installer when I boot from the generated ISO:

"No kernel modules were found. This probably is due to a mismatch between the kernel used by this version of the installer and the kernel version available in the archive."

I find that simple-cdd is generating the iso with the following kernel:
Linux ... 5.10.0-7-amd64 #1 SMP Debian 5.10.40.1 (2021-05-28) x86_64 GNU Linux

However the host system (recently apt upgraded) has the following kernel:
Linux ... 5.10.0-8-amd64 #1 SMP Debian 5.10.46.2 (2021-07-20) x86_64 GNU Linux
(note the date on the kernel is only 2 days prior from when I ran into this issue)

I am not specifying mirror/codename nor mirror/suite in the preseed that simple-cdd is using.  My understanding is this allows debian-installer to install whatever version ends up in the generated iso's initrd.  I also tried again with these values enabled and set to "bullseye" however the problem remained.

Searching for this error I find that other people that have had the same issue in the past.  In past bug reports this seems to have been fixed somewhere in the distro, so I'm reporting it here.

Since this problem seems to come back every now and again, I'd also like to know if there is a workaround that people can put into their simple-cdd config to allow things to keep working when the kernels occasionally get out of sync like this.  If that's possible, it might be good to mention that workaround here, for future searchers.

Thanks!