watch won't stay connected to iPhone

My wife has the original apple watch 38mm, when we updated the software on it and her iphone 6+ to watchos 3 and iOS 10, the watch will no longer stay connected to the phone via bluetooth. Turning bluetooth off and then on again on the phone reconnects them for a short period of time, but within a few hours, they disconnect. I have had no issues with my watch (42mm original) and phone (6+) running the same operating systems. I've tried re-pairing the watch, and I've tried restoring it as new, and nothing seems to work. Anybody else having this issue?