Welcome to the community, Miengoarie96!
I understand how frustrating it is to suddenly lose connection while traveling. Here are the two most likely reasons based on how the Sunrise backend handles US roaming:
First you can check in the Sunrise Cockpit via a Wi-Fi network. Sunrise has a built-in data roaming safety limit that is often set to 50 or 100 CHF by default. If your phone uses up this budget in the background during your first two days Sunrise automatically blocks your SIM/eSIM from registering on any US mobile network to prevent extra costs. You can easily increase or adjust this monthly roaming cost limit directly in the free Sunrise Cockpit and it should work again within a few minutes.
Cost control abroad (roaming) | Support
Another reason could be the VoLTE roaming configuration. Since US carriers completely shut down their older 3G and GSM networks your phone needs to use 4G or 5G with VoLTE enabled to establish a connection. If increasing your roaming cost limit does not solve the problem you can contact support via Wi-Fi chat or use another phone to call the hotline from abroad at +41 58 777 01 01 (Mon - Sat 08:00 - 22:00, Sun 09:00 - 22:00) to ensure that VoLTE roaming is correctly provisioned for your eSIM profile on their backend side. More contact options can be found here:
Sunrise help and contact
Cheerio, cosmo