I can pair my watch to my Ulefone S9 Pro. It will work as it is supposed to for a while. Whilst the Wifi is connected (at home) the watch seems to remain connected. When I leave the house, after 5-10 mins it loses connection unless I turn the screen back on. Smart notifications stop working. After a day or 2 at most I get a notification on my phone that Android Notification service has stopped unexpectedly and I should reboot my hone for it to work. After rebooting, watch will appear to be connected but there is no way to ever get another notification without removing device and repairing. Sometimes that won't work and I have to uninstall the app and start again. I have tried all the tips that Garmin give on the help page including doing a factory reset on the watch. It is driving me crazy!!
So after speaking with Garmin they basically said it's nothing to do with them and it's the fault with the model of phone. They didn't back that up with any evidence and when I asked what the fault was, all I was provided started with "well the only thing I can think is....." So they don't know what the fault it but don't want to do anything. I wish I could say I'm surprised......