vivoactive 4 (all versions) SW 5.10

Yes. I just hope the device stays on V5.0 now and doesn't update by itself. 

Did you revert to 5.0, factory reset, restore settings or set up watch again? ... and you're now still having battery drain?

Yep rollback to 5.0, factory reset and settings restored. Still having battery drain, none of the sensor seems to not be working. For example SW version of the HR monitor is at 0.00

This is really crap. I would not say a word if this was some Chinese product for 20 euro but when paid such amount of money I expected some level of quality... 

After first disappointment with battery consumption a spent like two months with carefully changing the settings one by one and installing all my watchfaces, widgets and datafields one ofter one just to find out if something cause battery drain till I finally get balance between performance, functions and battery performance. It took a lot of factory restarts and doing all the work again...

Now one update and I am back at 50% per day consumption (before it was between 0.5% to 0.8% per hour). Keep your updates Garmin, there never been any significant benefit between versions, major issues (like stupid lock behavior) are left without any sign of interest and we just have to worry what will go wrong with new update.

Icing on the cake: how bad SW engennerig at garmin has to be is demonstrated by feature where set alarm is overridden by automatic update. It is so nice to wake up one hour after your 300 euro watch should have wake you up, looking on the screen to see there is only information about new update (which probably ruined your watch) and no sign of alarm which you set in the evening... 

I've gone from 0.75% battery usage per hour to anywhere from 1.5% to 2.5% battery usage since this update.

I have only had the watch a few weeks but I assume there is a formal way to call in for support? Has anyone done that?

Factory reset didn't help

I've gone back to 5.0 using Martin's instructions

Took a little while to settle after that, but seems now to be back to previous battery usage (lasting 5-6 days)

I also got the notification for available update after this, but as per Martin's suggestion opened the GUPDATE.GCD file (found in /GARMIN folder) with a text editor and deleted the contents.

The only hassle I had was that I was  initially unable to re-setup Garmin Pay. Eventually had to unpair VA4 in GCM/ uninstall GCM from phone/ reboot phone/ reinstall GCM/ add VA4 device back, and was then able to complete setup of Garmin Pay

I've used the contact form on the garmin website, you also have the option to call.

M'y VA 4 works fine with Fw 5.1.