Raspberry pi 3 Wifi issues on poor signal

Hello,

have you tried setting autoconnect-retries=0 in your connection configuration file to see if that helps?
You can read more about the network configuration here:
https://docs.resin.io/deployment/network/2.0.0/#introduction

and you can read more about the NetworkManager options here: https://developer.gnome.org/NetworkManager/unstable/nm-settings.html