I have two SIM cards.
Sim1 should be used for mobile data while sim2 should be used for phone calls.
When only SIM 1 is inserted, mobile data works.
When both SIM cards are inserted, mobile data goes only via sim2. Even if I disable mobile data on SIM2 and enable it on sim1, as soon as I turn on mobile data in the dropdown, SIM2 is re-activated and used for mobile data.
I also tried switching the SIM slots, same result.