Heart Rate stops at Night, lost Bluetooth Connection some times

Hello,
some times the heart rate on my 5 plus stops a few times at night for 10-20 minutes.
And some times, heart rate at night works great.

And some times my Bluetooth connection ist on but I receive no messages from my phone.

What can I do to fix?
i have allready reset my watch and phone.

Thanks in advance.

Manuel
and sorry for my bad English