AWatch restart randomly after every update

It began with the 5.1.2 update, after that my Apple Watch restart randomly in loop, it stay on for about three minutes, then restart.

It restart only when it's connected to the iPhone...when I turn it in Airplane mode it doesn't restart.

I try to restart both iPhone and Apple Watch, but nothing change.

i delete all third app from the watch, but nothing.

Reset network setting on iPhone, nothing.

When I update to 5.1.2, I also unpaired AW and iPhone...when I tried to pair again, immediately after the alignment of the viewfinder, the apple watch restart!so they don't pair...

i also try to send it at the support, but they resend me and said it's all ok!

after 3/4 day of failed attempts, it works!

but now with 5.1.3 update, I have the same problem!

can anyone help me?

thanks a lot