As identified in MDL-63316, the participants table in 3.4 and 3.5 is default sorted by first name. The fix suggested in that MDL-63316 is sufficient to resolve the degradation of behavior between 3.3 and 3.4/3.5. However, a better solution would be to implement an admin setting which controls the default sort field for the participants table.

This was identified as a possible improvement in MDL-51265. I'm creating a new issue to target more recent versions of Moodle.