Mine is on GVK4. Got this watch update a few days ago and was surprised to find my watch flat the next day (as in COMPLETELY flat) at a time of day I would normally have loads of battery left. I have tiny wrists so am wearing the 40mm galaxy watch 4 which does have a smaller battery life than it's bigger brother. Anyway I should have been OK for another 10-11 hours. After I charged it from 0, I noted I was losing 20% of battery every hour, which is obviously not satisfactory! I was going to google for similar experiences in the coming days but the problem appears to have sorted itself before I got the chance to do a search. I'm now getting slightly better battery life than previously. It wasn't clear at all in the battery info what was causing it. There was no apps that had suddenly become very blood thirsty, all app usage was was as expected & as previously. Maybe it needed time to bed this new update in (for lack of a better more technical term). Not sure if I ever had the GVI3 firmware. I expect I did as I usually download all updates soon after being offered them. Luckily I didn't have the issue myself if I was on that version previously.
Sorry to hear of your experiences, but good to hear that the retailer are now following up with this as they should.