invalid-function (date date) after update to 9.5

[Florian Lindner]

Hello,

after the upgrade to 9.5 (9.5-g0a86ad @ /home/florian/.emacs.d/elpa/org-9.5/) 
on 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20, cairo version 
1.16.0) of 2020-09-19 my agenda stopped working

(org-agenda) -> any keyword (a, t or n) gives:

Debugger entered--Lisp error: (invalid-function (date date))
(date date)()
org-agenda-get-day-entries("/home/florian/org/capture.org" (10 4 2021) 
:deadline :scheduled :timestamp :sexp)
apply(org-agenda-get-day-entries "/home/florian/org/capture.org" (10 4 2021) 
(:deadline :scheduled :timestamp :sexp))
org-agenda-list(nil)
funcall-interactively(org-agenda-list nil)
call-interactively(org-agenda-list)
#f(compiled-function () #<bytecode 0x12e5d8d>)()
funcall(#f(compiled-function () #<bytecode 0x12e5d8d>))
(let nil (funcall '#f(compiled-function () #<bytecode 0x12e5d8d>)))
eval((let nil (funcall '#f(compiled-function () #<bytecode 0x12e5d8d>))))
org-agenda-run-series("Agenda and all TODOs" (((agenda "") (alltodo ""))))
org-agenda(nil)
funcall-interactively(org-agenda nil)
call-interactively(org-agenda nil nil)
command-execute(org-agenda)

When I move capture.org out of the way, it happens to another file. Any hint 
what can be the problem here or where I can start looking?

I have seen the problem mentioned in 
www.reddit.com/r/DoomEmacs/comments/mlc7qi/orgagenda_stopped_working_after_upgrade/
 but that basically says to reinstall. I deleted my elpa folder and 
reinstalled, but nothing changed.

Thanks!