Based upon the information on the previous page, there could have been an ear clearing issue or not enough weight. Neither one is normally a serious problem. If required, the buddy team can surface and deal with the issue, get more weights, etc.
The comments made about buddy teams staying together is important. If the divemaster is not there then the buddy team needs to rely upon their training to deal with the situation...which may mean surfacing and ending the dive.
A new diver is not going to be as experienced and able to handle new problems and stresses like a seasoned diver who has had many dives and lots of additional training. I assume that training at least gives the diver the ability to surface carefully...listening for nearby boats.
The other point to consider that may go a long way to reducing these events is to have a divemaster along with novice divers new to Cozumel. There are multiple things that new divers need to learn to become comfortable with drift diving. I suspect that in two dives with a divemaster/instructor, those skills can be taught and practiced.
As an example, a buddy team needs to be able to safely surface if separated from the group. They can practice that under the supervision of the divemaster/instructor at the end of the dive. Ascend a do a safety stop around 15 feet. Deploy their surface buoy if that is reasonable, listen for boats and surface. Add air to the BC and monitor for boats, inflate the surface marker if they did not while underwater and wait to be picked up.
I am a firm believer that divers should be able to safely ascend SOLO. That too can be practiced in a simulated mode under the supervision of the divemaster/instructor.
Between learning drift diving skills and staying with your buddy, the "missing diver" events should be greatly reduced.