Cant really comment on the plug. I do have a Kwickset 910 and mine has been pretty reliable, if I recall I did need to get it close to the Hub to get it to pair the first time. I would suggest getting a cheap wireless access point that way you can bring your hub to your lock. There are some pretty cheap ones out there.
Sounds like a mesh issue, bunch of threads on trying to improve it. It can be tricky.
I assume your on a C5 or earlier since you say you been running it for a few years. If on a C7, however, there is a nice tool that allows you get a little better view of how thing are routed.
