connection to android phone issue after upgrade to firmware version 8.3.0

I have a Surf Solo router. I just upgraded firmware to 8.3.0. The router is detected by all of my devices (using wifi on Cell phones, computers, smart TVs) and the signal is excellent. However, the router was not recognizing the wifi password. I did not change the wifi password.

After going through all possible passwords, I decided to try the last 8 characters of my router’s MAC address and it worked!

Do you know what happened and can you recommend how to change from the MAC password to a new wifi password without recreating this problem. I am tempted to keep using the MAC address, but I don’t want to do that on insecure devices like TVs.

Any of your wisdom would be appreciated!