I cannot find a candidate CL for this.

This one was merged before the failure started:

https://chrome-internal-review.googlesource.com/c/chromeos/overlays/overlay-amd64-generic-cheets-private/+/652771

CL:*652771 is for a specific board (amd64-generic-cheets) which isn't used by any dragonegg related boards.

i agree it looks like the same bug.

This seems to be the CL that caused the issue:
https://chromium-review.googlesource.com/c/chromiumos/overlays/board-overlays/+/1148550/4/baseboard-dragonegg/profiles/base/make.defaults

But, yeah, we should add a blocker, or wait for the paladin builder to clean itself up (isn't it supposed to do that and start from a clean chroot when it fails a few times in a row?)

+ Rajat, Shelley - can you find someone to own this? 
I am this week's sheriff, and it is still failing. 

I don't think I understand the issue, but I anyway have a CL out to disable TPM (for now):

https://chromium-review.googlesource.com/c/chromiumos/overlays/board-overlays/+/1164531

For the actual fix for the underlying issue (having ability to switch from USE=tpm to USE=tpm2 without clearing /build/$BOARD, if that's how paladins buil): let's move discussion to  issue 728863 , where this one was merged.