"ssh-keygen -K" returns "invalid format" when restoring FIDO2 ssh keys on a new machine

Prerequisites

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• Make sure you are able to repro it on the latest version
• Search the existing issues.

Steps to reproduce

I have an SSH key stored on my FIDO2 security key (Yubikey), and a new work laptop to set up.
I'm running ssh-keygen -K to regenerate the key handle file, but the command fails with Unable to load resident keys: invalid format after submitting my FIDO2 PIN.

Unfortunately the logs don't give enough information to debug this further so I'm a bit stuck. Any help would be appreciated.

Expected behavior

PS C:\Users\nikn\.ssh> ssh-keygen -K
Enter PIN for authenticator:
You may need to touch your authenticator to authorize key download.
<LOAD_RESIDENT_KEYS>

Actual behavior

PS C:\Users\nikn\.ssh> ssh-keygen -K -vvv
Enter PIN for authenticator:
You may need to touch your authenticator to authorize key download.
debug1: find_helper: using "C:\\WINDOWS\\System32\\OpenSSH\\ssh-sk-helper.exe" as helper
debug3: Creating process with CREATE_NO_WINDOW
debug3: spawning "C:\\WINDOWS\\System32\\OpenSSH\\ssh-sk-helper.exe" as subprocess
debug3: start_helper: started pid=25496
debug3: ssh_msg_send: type 5
debug3: ssh_msg_recv entering
debug1: client_converse: helper returned error -4
debug3: reap_helper: pid=25496
Unable to load resident keys: invalid format

PS C:\Users\nikn\.ssh> ssh -V
OpenSSH_for_Windows_9.5p2, LibreSSL 3.8.2

Error details

Environment data

PS C:\Users\nikn\.ssh> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      5.1.26100.7462
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.26100.7462
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

Version

OpenSSH_for_Windows_9.5p2

Visuals

No response

Start with the ssh-keygen -K resident-key restoration path and the ssh-sk-helper.exe interaction shown in the verbose log. Compare the helper's returned error -4 with the invalid format result on OpenSSH_for_Windows 9.5p2. Done means reproducing the failure, identifying its cause, and confirming that resident FIDO2 keys can be restored successfully.