Off list you've sent me a very normal looking heading with a
property drawer. The error seems to be right after
":PROPERTIES:". I see nothing that should cause this error.
Are you able to reproduce this error?
If so, I would love to get an actual backtrace. The warning has
backtrace: nil. I'm not certain why it's nil but possibly it's
because the backtrace library wasn't loaded.
Typing 'M-x load-library RET backtrace RET' should load it.
It's also quite possible this bug has already been solved with a
recent version of Org mode. You're on 9.7.11 while the latest
version it 9.8.12. The newer version seems to offer a couple
property drawer fixes and slightly more checks in org-element.
You can refer the Org manual on how to install the latest version
"(org) Installation".
