I had this problem with “Sim Card removed” several times last week with my XA2 on a short vacation in Italy.
1st time on the outward journey when crossing the border from Germany to Austria.
2nd time hiking in South Tyrol.
3rd time on the way back when crossing the border from Italy to Austria.
At 1st and 3rd I had to restart the phone.
This is very inconvenient if it causes the navigation to fail and you have to restart the phone while driving.
With 2. the message disappeared again after a while. I have no idea what SFOS was doing or restarting, but all apps were suddenly closed and the home screen was blank. But it wasn’t a complete restart.
I had the phenomenon with the blank home screen 1-2 times that day, possibly due to poor reception in the mountains.
My provider in Germany is Vodafone. Roaming network in Italy was Vodafone IT. Roaming network in Austria was A1.
Another effect of “Sim Card removed” was, in my experience, that GPS reception no longer worked.