Hi,

recently a bug has been reported to me (it is marked as closed
now, but only in Eldev itself, in that I added a workaround for
it):

    https://github.com/doublep/eldev/issues/52

I managed to reduce the way to reproduce it to a fairly short piece of
Elisp code that doesn't depend on Eldev, i.e. is "pure". The
workaround I used is also present in the attached script, but
commented out.

In short:
- run attached script as

    $ emacs --batch --load bad-request.el

  using Emacs 26.x (important!);

- observe that it dies with error
  "https://elpa.gnu.org/packages/org-edna-1.1.2.tar: Bad Request"

The script tries two install two packages (Org and Org-edna) from GNU
ELPA.  The second download dies with the error shown above.  If the
workaround line is uncommented, i.e. if HTTP(S) connection to GNU ELPA
is *not* reused for downloading the second package, it succeeds.

I'm not sure if it is a bug with GNU ELPA, Emacs 26 or something else.

Paul