For reference - https://tracker.moodle.org/browse/MDL-62709.
Installing and upgrading help
Moodle 3.5 - Messages Migration Message
Saw this after receiving an email from a client, when do you think a patch will be published to address the issue? Apparently this has been fixed in Moodle 3.5.1, but the code has not yet been published on moodle.org. Thanks.
It is available in the weekly release from https://download.moodle.org/releases/latest/. 3.5.1 will be the latest official update of Moodle 3.5 that contains the patch, but you can get it beforehand by choosing to download the weeklies (even though the version isn't actually 3.5.1).
I know this can be a bit confusing.