Boise Ed attempted to submit a Tundra comic, using a link from The Seattle Times. Reading between the lines of his comment (see below), the comic he meant was probably all or part of this one:

Here’s what Boise Ed wrote: He says “a while ago,” but I think the walrus joke appeared just a couple of days earlier. There doesn’t seem to be an accessible archive where I can check on that…. Is there any other source to see the Tundra strip?

The answer is (probably) “No, there isn’t.” The problem is that both The Seattle Times and the official Tundra website provide only the strip for the current day. Past Tundra archives are only available on a pay-to-view basis (to Patreon members). This means that any Tundra link sent to CIDU has an expiration limit of (at most) 24 hours, which renders those links useless for all practical purposes. Therefore, if you want to submit a Tundra comic, don’t depend on the link: send a screenshot, or attach a graphic file.

P.S. The same problem exists for all Arcamax comics. The Arcamax links are not quite so ephemeral, but they do expire after just a couple of weeks, so it’s not a good idea to use them for submitting CIDUs, nor for embedding any images in comments.