Comment (by Zach Etienne):

Hi Edwin

It seems that when you followed the Download instructions there were errors in downloading certain thorns (the errors you shared indicate they do not exist). I know this can happen if you are behind a firewall. Please follow the download instructions again, but first make sure you have the ability to clone the needed repositories. One thing you could first check is if you can access fftw.org .

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2535/et_2020_11-build-issue