Remember to cover the basics, that is, what you expected to happen and
what in fact did happen. You don't know how to make a good report? See

https://orgmode.org/manual/Feedback.html#Feedback

Your bug report will be posted to the Org mailing list.
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My org-agenda-custom-commands contains

(" " "Notes" tags "NOTE"
  ((org-agenda-overriding-header "Notes")
   (org-tags-match-list-sublevels t)))

notice the key is "SPC" in this case, it used to work without issue. however
after a recent update of spacemacs and package update
(org-plus-contrib-20191230). It suddenly stopped working.

And in the later version I also tried -20200206, it is still broken.

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This issue is initially reported to spacemacs as issue 13138 - SPC no longer works as a custom agenda command key in org-mode, after some investigation, it it highly possible that here I quote:

A possible reason why the behavior changed might be because of this commit from 2 months ago:
https://code.orgmode.org/bzg/org-mode/commit/80b29acba3847c1756fa3c143d6991964f7273ca

agenda: Enable navigation for the agenda dispatch buffer

lisp/org-agenda.el (org-agenda-get-restriction-and-command): Use
keys C-n, C-p, SPC, DEL analogue to export dispatcher. See function
org-export--dispatch-action.

Reported by Nathan Neff https://lists.gnu.org/archive/html/emacs-orgmode/2019-10/msg00179.html.

Could those agenda navigation keys made configurable? Or an option to disable the newly introduced navigation if not needed?

Best Regards,

Yuan

Emacs : GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.10)
of 2019-08-29
Package: Org mode version 9.3.4 (9.3.4-elpaplus @ /home/lin/.emacs.d/elpa/26.3/develop/org-plus-contrib-20200206/)