I have the same problem. I have a Huawei Mate 10.
It has been working fine until the last update.
I have reset it 4 times now and it is still the same. Battery life is really bad too.
If I open my phone it disconnects, also when I open the camera on my phone, open my browser and on top of that it randomly disconnects even when I'm not doing anything.
The worse part I'd that it will not automatically reconnect.
Have a look on Google play as sooo many have the same problem.
Im not sure if anyone else has mentioned this, but it's worth a try.
Turn the watch off.
Hold down both buttons until you see the rebooting message.
Then release the buttons.
This clears the cache and now my watch does not disconnect so often, when it does it reconnects quite quickly.