Erf... I'm sorry this fix doesn't apply to your case, I really thought every one on this thread was having the same problem.
Maybe you can try this, it won't provide you with a solution, but it should give information on the issue :
-
Run the "locale" command just to double-check everything is "en_US" or "en_GB"
-
Follow the steps to revert to master branch
sudo rm /etc/pihole/ftlbranch
pihole checkout master -
Type the following command and write down the the date / time of the "/etc/.pihole" directory :
ls -la /etc/ | grep "\.pihole" -
Wait for a few minutes (at least one)
-
Confirm your PiHole can access the Internet (ping google.com for example)
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Follow the steps to install beta version (echo "FTLDNS"... pihole checkout...), it will fail again
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Then run the
ls -la /etc/ | grep "\.pihole"again and compare the date / time with the one on step 3
If the time of this directory has changed, it should indicate that the new sources have been fetched. This is in no way a "scientific" test, but that should give a clue whether the issue happens when fetching the sources or later. Alternatively you can use "du -h /etc/.pihole" on steps 3 and 7 to get the size of the directory and see it has changed.
If I get this correctly (devs please correct me if I'm wrong), the "pihole checkout" command first fetches the selected branch sources through GIT, then runs the installer located in "/etc/.pihole/automated\ install/basic-install.sh", but as there is no "verbose" mode, the error looks exactly the same whether the update fails during sources fetching or when running the installer.
But if the time (and / or size) of the ".pihole" directory was modified, this should indicates the fetching sources step went OK, but the installer failed later (for example when your locales are not en_GB / en_US in my case).
Then maybe you can try to manually run "sudo /etc/.pihole/automated\ install/basic-install.sh" and see if it displays more detailed errors or anything that could help identifying the issue (but wait for a dev to confirm - or not - that there is no problem with manually launching the installer and it won't break your PiHole).