Using International Roaming in Japan - torubleshooting

Hi, I am in Japan right now and I have the T-Mobile Magenta plan using iPhone 13.  I have been using data roaming and it generally works well, but after about a week, all of the sudden the internet stops working.  Even though there are signals (3 or 4 bars) but internet and text do not work, and I can’t even use google map to navigate.  I tried to reset my phone several times but nothing works.  I checked my data usage and only 2.4GB was used so far (and I thought I have the 5 GB cap).

Can anyone assist?  Did I mess up the setting or something?  Or does Japan have a different bandwidth cap?

And when does the cap reset?  Is it the first of every month or based on the billing cycle?

Any help is much appreciated.