Try restarting both the watch and the phone and see whether it helps. Make sure the app has granted all required permissions. When it misses some of them, it may be cycling in some power consuming loop.
I had the same when I was in the beta for the new layout.
One of the reasons I quit the beta (and the new layout is just rubbish). Guess now that the new layout is permanent, more people will find the battery drains.
Restarting both watch an phone only stops this behavior temporary.
I am using the beta version since around 2 months, and now the v5 without any issues. The battery consumption of the app for the last 10 days is at 5.4%, still less than for example WhatsApp, despite that I use it permanently and rather intensively.
... another thing that can increase the battery consumption considerably, is a pending update. If there is transmission problem, low room on the storage, or another problem with the update, the process may be looping as well, and cause a battery drain both on the watch, as well as on the phone. You can usually fix it by connecting the watch over the USB cable to a computer with Garmin Express, checking for updates, and installing them if any are available.
