If you try to use Fossil 1.37 — the last 1.x release — to clone a repo that has SHA-3 hashed artifacts in it, it says, "server returned an error - clone aborted". Since 1.37 pre-dates this feature, it can't give a more detailed diagnosis than that.

If you have an old clone made from before the transition and try to update it, I'm not sure what it says, since I don't have any of those around any more. It has, after all, been three years since Fossil began to move on this problem, so that it's largely a past issue for us now.

This transition time was indeed annoying for us over in Fossil land, but Git's going to have to go through a transition like this, too. The question isn't whether but how long we'll have to wait for it to begin and how long it'll take to complete.