Can't create generic/centos8 box with SSH keys loaded

I'm trying to launch one each of the generic/centos{6,7,8} boxes using Vagrant & Virtualbox. The 6 & 7 boxes launch fine, but the 8 box will not start up if I have any SSH keys loaded in my agent. It just logs "default: Warning: Authentication failure. Retrying..." over and over until I run ssh-add -D to remove all SSH keys from my agent.

It only seems to affect the vagrant up action, once the machine is booted I can load all of my keys again and I can vagrant ssh without any problem.

Here's the Vagrant output:

$ vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Importing base box 'generic/centos8'...
==> default: Matching MAC address for NAT networking...
==> default: Checking if box 'generic/centos8' version '3.2.24' is up to date...
==> default: Setting the name of the VM: generic-centos8-0_default_1623658922049_63268
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
    default: Adapter 1: nat
==> default: Forwarding ports...
    default: 22 (guest) => 2222 (host) (adapter 1)
==> default: Running 'pre-boot' VM customizations...
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
    default: SSH address: 127.0.0.1:2222
    default: SSH username: vagrant
    default: SSH auth method: private key
    default: Warning: Authentication failure. Retrying...
    default: Warning: Authentication failure. Retrying...
<RUN `ssh-add -D` HERE>
==> default: Machine booted and ready!
==> default: Checking for guest additions in VM...
    default: The guest additions on this VM do not match the installed version of
    default: VirtualBox! In most cases this is fine, but in rare cases it can
    default: prevent things such as shared folders from working properly. If you see
    default: shared folder errors, please make sure the guest additions within the
    default: virtual machine match the version of VirtualBox you have installed on
    default: your host and reload your VM.
    default: 
    default: Guest Additions Version: 5.2.44
    default: VirtualBox Version: 6.1

And this is what the box is logging during the authentication failures:

Jun 14 08:22:34 centos8 sshd[1226]: Connection closed by authenticating user vagrant 10.0.2.2 port 62027 [preauth]
Jun 14 08:22:34 centos8 sshd[1228]: Connection closed by authenticating user vagrant 10.0.2.2 port 62041 [preauth]
Jun 14 08:22:34 centos8 sshd[1230]: Connection closed by authenticating user vagrant 10.0.2.2 port 62045 [preauth]
...

Vagrant version: 2.2.16 Box version(s): 3.2.24

lavabit / robox

Can't create generic/centos8 box with SSH keys loaded #202