My new LEM X would not connect via supplied USB charge / data lead.
I checked the MTK drivers.
I continuity tested the lead (it is data and power - as I expected for the LEMFO supplied lead).
I scratched my head, and worried that I am an idiot (it does happen).
I put on my extra glasses and inspected the contacts on the watch.
Then, I poked at the contacts with a sim tray tool.
Guess what?
There was a thin layer of transparent glue across half of one of the centre (data) contacts.
It covered just enough of the contact area to stop the spring-loaded terminal from making electrical contact.
I scratched it off.
Now it works.
HTH