First of all, how are you measuring signal strength? I'd suggest using signal strength as reported by the Access hub by accessing it's IP address from a web browser. That indicator seems to be pretty close to real time as opposed to the signal strength bars on the Myacurite dashboard that do not appear to be real time. (delayed or rolling average???)
Now make some small adjustments to the location of the Access hub. Move it around, lay in on it's side, point it in various directions. I've found that small changes can have a big impact on signal strength. (even as small as a few inches). I don't know what else to suggest. Maybe you're experiencing some interference from something else in the area.
RF can drive a person nuts at times. It seems to be about 50% science and 50% luck. My solution was adding an external antenna which has made it rock solid.