After git bisect, I found the bad commit:

#+begin_example
0ef88e2d9 * | bad @ org-agenda.el/org-agenda-get-scheduled: Use cache
#+end_example

after org-agenda generation, lot of entries not displayed. Then I found lot of errors in =*Messages*= buffer.

#+begin_example
Wrong type argument: stringp, (timestamp (:type active :raw-value "<2021-02-28 Sun>" :year-start 2021 :month-start 2 :day-start 28 :hour-start nil :minute-start nil :year-end 2021 :month-end 2 :day-end 28 :hour-end nil :minute-end nil :begin 7679 :end 7696 :post-blank 1)); Skipping entry
Wrong type argument: stringp, (timestamp (:type active :raw-value "<2021-02-28 Sun>" :year-start 2021 :month-start 2 :day-start 28 :hour-start nil :minute-start nil :year-end 2021 :month-end 2 :day-end 28 :hour-end nil :minute-end nil :begin 11212 :end 11229 :post-blank 1)); Skipping entry
Wrong type argument: stringp, (timestamp (:type active :raw-value "<2020-06-30 Tue>" :year-start 2020 :month-start 6 :day-start 30 :hour-start nil :minute-start nil :year-end 2020 :month-end 6 :day-end 30 :hour-end nil :minute-end nil :begin 13781 :end 13798 :post-blank 1)); Skipping entry

......
#+end_example