Samsung Galaxy S10+ randomly switches to roaming SIM and forces enable data roaming!

I have the latest firmware update, and I'm using it with 2 SIMs; Sim #1 is a Google-Fi on roaming, and Sim #2 is the local default sim. I choose SIM 2 to be the default for everything (calls, SMSs, and data). However, I kept seeing the mobile for some reason switches the data to SIM 1, however, I disabled *data roaming*, and surprisingly, the mobile still randomly changes to SIM 1 (Google Fi) and also consume data!!