mirror functioning on one machine but not another

[AC]

I have TeX Live 2020 installed on a number of Linux machines, and updating regularly from various mirrors. As of today (Sun, Aug 30 morning EST) one of the machines hangs while trying to update from 

http://ctan.mirrors.hoobly.com/systems/texlive/tlnet

Output:

--- cut here ---

$ tlmgr update --self --all
---
Unable to download the checksum of the remote TeX Live database,
but found a local copy, so using that.               
You may want to try specifying an explicit or different CTAN mirror,
or maybe you need to specify proxy information if you're behind a firewall;                               see the information and examples for the -repository option at                                            https://tug.org/texlive/doc/install-tl.html
(and in the output of install-tl --help).                                                                 tlmgr: package repository http://ctan.mirrors.hoobly.com/systems/texlive/tlnet (not verified: unknown)    tlmgr: saving backups to $HOME/texlive/2020/tlpkg/backups

--- end ---

The above used to work just fine yesterday, say.

At the same time though, on a different machine (different network):

--- cut here ---
$ tlmgr update --self --all
---
tlmgr: package repository http://ctan.mirrors.hoobly.com/systems/texlive/tlnet (verified)
tlmgr: saving backups to $HOME/texlive/2020/tlpkg/backups
--- end ---

I am positive I'm not behind a firewall or any such thing. Other mirrors work, as did this one very recently.