If filesystem UUIDs are IP equivalents. Then device paths are MAC addresses. FS labels are DNS. Device mapper entries are service discovery.

“Invalid” or “unparseable” are more understandable descriptors in normal language. I don’t think I ever heard of garbage/junk being used for that in language theory but it may be domain specific usage.

It can still have issues with potential attacks that would redirect your client to a system outside of the VPN. It would prevent MitM but not complete replacement.

Likely you needed to include the intermediate cert chain. Let’s encrypt sets that up automatically so it’s quite a bit easier to get right.

Initrd contains the systemd binary and enough libraries, services, and kernel modules to get booted this far. The system failed at switch root which is where the real root disk is mounted. Initrd can contain as much or as little as needed to get a working system which can be a lot of you are using a network filesystem as a root for instance.