Summary: using org-clone-subtree-with-time-shift on an entry with the ID property and a timestamp causes an error or does not create different IDs, which worked before 27.1. Long Description: I have a calendar file with a lot of entries, but I slimmed it down to a MWE: === begin MWE === * my appointment with id :PROPERTIES: :ID: 048c5a49-1aed-45d4-b7a9-34caf4f13266 :END: <2020-11-15 Sun 15:30> example text === end MWE === I create such an entry routinely via a capture template with a timestamp and I add the text, and the ID is created with (add-hook 'org-capture-prepare-finalize-hook 'org-id-get-create). For repeating tasks, 10 weeks ago and before (i.e. before I updated to 27.1), I used to use `M-x org-clone-subtree-with-time-shift 10 +1w ` and I got 10 repetitions, each with a separate unique ID. I tried this now and I get an error "wrong-type-argument stringp nil", with the backtrace described below. If I change the order of the timestamp and the properties drawer in the MWE, I get the date-shifted clones but each with the same ID. In my calendar file with lots of entries, I still get the same error if I change the order, so I suspect that the function is context sensitive. Anyway to reproduce the error, 1. save the above MWE in an org file 2. open the file with emacs -Q 3. activate debugger with `M-x toggle-debug-on-error ` 4. run `M-x org-clone-subtree-with-time-shift 10 +1w ` The following backtrace is then produced: === begin backtrace === Debugger entered--Lisp error: (wrong-type-argument stringp nil) string-match("^/tmp_mnt/" nil) abbreviate-file-name(nil) org-id-add-location("9f1a8e57-e9be-42aa-a113-f8f478cc2a1b" nil) org-id-get(1 create) org-id-get-create(t) org-clone-subtree-with-time-shift(10) funcall-interactively(org-clone-subtree-with-time-shift 10) call-interactively(org-clone-subtree-with-time-shift record nil) command-execute(org-clone-subtree-with-time-shift record) execute-extended-command(nil "org-clone-subtree-with-time-shift" "org-clone") funcall-interactively(execute-extended-command nil "org-clone-subtree-with-time-shift" "org-clone") call-interactively(execute-extended-command nil nil) command-execute(execute-extended-command) === end backtrace === Emacs : GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.22, cairo version 1.17.3) of 2020-08-28 Package: Org mode version 9.3 (release_9.3 @ /usr/share/emacs/27.1/lisp/org/)