Comment by SahAssar

I don't see it in https://archive.org/details/worksofsirthomas0000urqu or https://archive.org/details/bim_early-english-books-1641-170...

I also don't find it on the site of "Klaus Schmeh" that it claims to be on a list of "Top 50 unsolved encrypted messages": https://klausschmeh.net/?s=Cyphral

Looks like the best source I can find is this: https://scienceblogs.de/klausis-krypto-kolumne/2014/11/17/we... which seems real-ish?