So you drew the sort straw... It's weird because I keep seeing this with GRUB, apparently misreading snapshots? But then it ignores the errors?
The easiest solution is to reinstall. Before you nuke the boot device, do you have a backup of your config? You'll want that handy first - so we'll need to go fishing for it if you don't.
Alternatively, if you want to take matters into your own hands and despise GRUB, you could instead use ZFS Boot Menu, which has the considerable advantage of not requiring GRUB's byzantine configuration - just plop the executable down in the EFI System Partition, boot to it, and it should automagically find the TrueNAS install.
Not a bad outcome. I have a server at work that's in that "nobody dares to touch it" state for fear of downtime, which I have to manually boot by telling GRUB at runtime what to do. Not fun, the team has an email with the commands and they're printed out and stuck onto the rack KVM unit. All because GRUB is ridiculous.