User cannot be added to FileVault unlock list after boot SSD migration

Might be more suitable for the broader Mac sub, but trying it out here first.

I'm on Monterey 12.6 with the following hardware:

Hardware: i7-10700K / Asrock Z490m / RX560 / 1TB FireCuda 530

I just migrated my system from a 500GB SN750 with FileVault enabled, to the FireCuda (APFS, no encryption), using Carbon Copy Clone's legacy cloner option.

Everything transferred nicely, and after 24h of testing key apps and making sure nothing was lost, I activated FileVault.

I have an admin account (let's call it ADMIN), a user (standard) account for daily use (call it PRIMARY), and a user (standard) account for family members who sometimes want a few minutes to get things done (call it SECONDARY).

I activated FileVault for the FireCuda within my primary user account. When booting now, I only get to unlock FileVault via the ADMIN account, and don't get to choose between ADMIN and PRIMARY like I used to. This means I have to unlock the drive, let the system boot into ADMIN, then log out and log in to PRIMARY.

When logged in (whether to ADMIN or PRIMARY), at the FileVault preference pane I only have the option to add SECONDARY to the list of enables who can unlock FileVault.

Any ideas?