* TODO My weekly task
  SCHEDULED: <2020-10-14 Wed +1w>

In daily agenda, if you mark the task done, which will cause the above to change into:

* TODO My weekly task
  SCHEDULED: <2020-10-21 Wed +1w>
  :PROPERTIES:
  :LAST_REPEAT: [2020-10-14 Wed 11:45]
  :END:
  :LOGBOOK:
  - State "DONE"       from "TODO"       [2020-10-14 Wed 11:45]
  :END:

But then if you run "org-agenda-undo" immediately in the agenda buffer, the task did not revert back to the original, instead, only the "LOGBOOK" part is gone, so it becomes this:

* TODO My weekly task
  SCHEDULED: <2020-10-21 Wed +1w>
  :PROPERTIES:
  :LAST_REPEAT: [2020-10-14 Wed 11:45]
  :END:

I don't think that's what people would expect from "org-agenda-undo", so it seems a bug to me.

This bug is also in orgmode 6.3.7, so likely has been there for a long time.

Thanks for looking into this.

Warren