Me too., same problem.
My Virgin Internet connections drops every other day for a couple of minutes and comes back ok. The WAN Router remains powered, just drops WAN link for a couple of mins.
The Yale hub is cabled directly into the Virgin router.
When the internet connection drops out the Yale hub goes offline, the app says it is offline (makes sense, but shame the app does not talk to the Yale hub locally when on the same network).
The problem is that when the Internet comes back, the Yale hub stays offline and will not come back on it's own - it needs manual intervention to power cycle both the power plug and internal battery off/on as previously described by op.
I view this as a Yale hub firmware problem.
I am now waiting for Yale support to answer my emails and searching for admin login to the Yale hub hoping I might be able to diagnose further.
Yale Smart Living Alarm