First of all 12mb (BSS Min Rate) is not related to data rate, it is management traffic rate and setting it to higher value forces a client to connect only to an AP, if it is able to send/receive management traffic with at 12mb speed.
To know more about BSS Min Rate, please refer below artilce.https://support.ruckuswireless.com/articles/000001657
Now come to the Echo Dot connectivity issue. Could you try creating a mobile hotspot from your mobile phone and try connecting the Echo Dot?
See if it connects fine on your mobile hotspot. If yes, then it means issue is specific to connecting on Ruckus Wifi. If not, then issue could be related to Echo Dot but not the Ruckus WiFi.
To troubleshoot on Ruckus WiFi, try forcing WLAN to broadcast only on 2.4 or 5 G and then try connecting Dot. Test this on both bands one by one and see if this resolves the issue.
For additional troubleshooting, you can use ZD troubleshoot utility. You just need to add Echo Dot's MAC address and start the troubleshooter and then try connecting the Dot to Ruckus WLAN.
You will see graphical representation of client connection to Ruckus WiFi and at what point it is failing. Also provide us a screenshot from the test, so that we can suggest additional troubleshooting steps (if required).
Syamantak Omer | Community moderator | Staff TSE | CWNA | CCNA | RASZA | RICXI | Follow me at https://linkedin.com/in/syamantak-omer-5949b6124