You do need to try simplifying the SSIDs and try them as the same and different.
So far my list of things to try are
1) Simplify SSID's ROUTERA = UPSTAIRS, ROUTER B = DOWNSTAIRS.
Same password ( will also try different passwords)
Then try SAME SSID Simplified - ROUTER A&B = MYHOUSE
2) Set ROUTERB as 192.168.1.230
(from google) - then on ROUTER A maybe use http://192.168.1.254/expert_user.html
And hopefully try to set the DHCP pool from 192.168.1.1 - 192.168.1.200
Reboot both Routers, try again.
3) - investigate the IPv6 and IPv4 - issue - once I understand the requirements.
Edited by deleted (Wed 15-Nov-17 15:03:16)