The turn order is not entirely dependent on Wits / initiative. In addition to some bosses going first by default, some can just go first the turn they show up, or they (or other opponents) have buffs that can increase their initiative or make them go first the next turn.
In general the preview for the next turn is always subject to change, based on a variety of skills or statuses that come into play in the current turn, characters being added to combat, or opponents killed, etc.
If the characters' turns are actually being skipped, do they still have magic and physical armour? Are they stunned or frozen, etc, so they are unable to do anything?
If there is no hard CC involved, please email supportdos2@larian.com with a save (or a Dropbox or Google drive link, etc) before the voidwoken shows up, where this can be reproduced.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder'.
