Why Data Sharing from Sim 1 gets disconnected when a voice call is in progress on Sim 2?

[Windows Central Question]

Am using Nokia Lumia 730, I use Sim 1 for 3G Data connectivity for Outlook/emails as advised by the dealer at the time of purchase and I use Sim 2 extensively for all Voice calls/SMS. the dealer had recommended and categorically stated that Sim 1 alone shall support the 3G and by default Sim 2 is 2G enabled etc.,

However when am sharing the Data over wifi with my Dell Laptop, the issue occurs whenever I receive a voice call on Sim 2, please advise, thanks

 

[rhapdog]

The issue is not just because of an issue of Sim 1 vs. Sim 2.

The way I understand things, at least the way it was explained to me (take with a grain of salt, as I'm not the originator of the info), is that when you take a call, the radio switches to that other band. The hardware can't do 3G on one band while doing 2G on another band. People using LTE data sharing will have the data downgraded to the next highest signal the phone will support. On 4G, you may downgrade to 3G. If on 3G, you may get the data dropped.

Perhaps someone else can confirm or deny this information.