I haven't ran the submersible missions that much but I've failed a syndicate rescue twice because the rescue target went into the water. The first time I was checking if there were any medallions in the underwater and I Instantly failed. The second time was when I found a medallion by a pool of water and the rescue target walked into the pool of water, failing me again. This bug is really frustrating as it wastes all the time I spend trying to find medallions. Not sure if this is intentional or
Yup, just happened to me. Syndicate NPCs could also dive in and drown. I can't seem to recreate that anymore maybe they fixed the NPCs. Now it's the hostage's turn.
Edit:
Had yet another rescue syndicate in Uranus today. The hostage pathing AI will actually consider taking a shortcut by going in the water to reach me despite me not going in it at all. Just being near a submersible hole is dangerous.