When review comments are bridged to a mailing list they can sometime end up in different order in different e-mails (all comments are present, they are just in different order). See for example:

https://mail.openjdk.java.net/pipermail/hotspot-dev/2020-September/042950.html

and the reply:

https://mail.openjdk.java.net/pipermail/hotspot-dev/2020-September/042955.html

See how in the reply the comment "This cleanup does not seem related?" is listed first but in the original e-mail the comment "This cleanup does not seem related?" is listed last.

There is probably a HashMap and/or HashSet used somewhere, they have non-deterministic iteration order.