It shouldn’t be an issue with 2G, 3G.
Something affects the card.
The other card that works fine at second slot it’s a 4G card, but still works fine as 2G when used at second slot.
So, I checked with the sim supplier.
The card works only as 3G. So, as long as the 2nd slot is only for 2G, the card cannot work directly.
Has anyone found anyway to change the 2nd slot for operating only at 2G?