Thanks for pointing this out. We fixed the problem with empty canisters in this updated frontend: https://history.ic0.info/
A warning: the backend changed as well, so if you added canister ids to the tracking then you will have to add them again. And you will lose old history from before the last 20 changes. This will happen again until we deploy the final version of the backend. It is still under development right now.
If anyone has been tracking anything meaningfully in any old version of the backend then please let us know.