Fail2ban does not block access from android phone

[wmd1942 4]

I set up fail2ban on my Linux server which monitors emby log file. It works on all devices except my android phone (Samsung S20) with T mobile wireless service. After specified number of failed login attempts to my emby server with Emby android app, the fail2ban status shows the IP address, xxx.xxx.123.166, had been banned. However, I'm still able to log in (if the correct credentials are provided). The weird thing is the IP address from IP lookup service (through web browser) shows my phone's IP address is xxx.xxx.123.148. Both IP addresses are from T mobile in the same region. I wonder if anybody had the same problem. If so, how it could be resolved? Thanks.

Edited December 29, 2022 by wmd1942
clarification

[UCM_1 10]

I don't know specifics for the T-mobile network, but typically the publically visible IP address can often change when you are using a cellular network.

[wmd1942 4]

If I used the web browser of my phone to fail the login intentionally, fail2ban works. The emby server shows the banned IP is IPv6 address, which is the same as what IP lookup service reported. Is there a way to force Emby android app to (or prefer to) use IPv6 address?