Error when running `elfshaker extract`: *FATAL*: Some files in the repository have been removed or modified unexpectedly!

[HighCommander4]

After trying to follow the instructions at https://github.com/elfshaker/manyclangs#x86-64, when I get to the elfshaker extract command, I get the following error:

$ elfshaker extract 20211130-02660T231245-9b704d31b54a616 [WARN (main) 130.625487ms]: File /home/nr/manyclangs/link.sh is more recent than the current HEAD! [ERROR (main) 132.172898ms]: FATAL: Some files in the repository have been removed or modified unexpectedly! You can use --force to skip this check, but this might result in DATA LOSS!

I don't really understand the error -- what repository is it talking about?

As best I can remember, I haven't done anything since a previous occasion when the command was successful, besides downloading a different month's set of builds.