The network of the primary SIM card is affected when the secondary SIM card receives SMS and MMS messages

Problem:

When the secondary SIM card is receiving SMS messages or downloading MMS messages, the mobile data service of the primary SIM card is temporarily interrupted and 4G or 5G may downgrade to 3G or 2G, as indicated by the network icon displayed next to the signal bars. After the secondary SIM card has received the SMS message or downloaded the MMS message, the 4G or 5G network of the primary SIM card goes back to normal.

Cause:

Your phone supports dual-card dual-standby single-pass. This indicates that only one SIM card can work at a time on the phone, resulting in your phone giving priority to SMS and MMS messages being received and downloaded on the secondary SIM card, while the network on the primary SIM card is interrupted.

Solution:

1. Open Messaging, touch , go to More > Settings > Advanced or Settings > Advanced, and set Auto-retrieve MMS to Off.

   If Off is selected, you can download MMS messages received on the secondary SIM card manually when you are not using the primary SIM card for accessing the Internet.

2. If your phone supports dual-VoLTE dual-pass, it is recommended that you enable the VoLTE function for both SIM cards. After that, both SIM cards can work at the same time in an area with VoLTE coverage and when the icon is displayed on the status bar.
   

   You can contact the Huawei customer service hotline to check whether your phone supports dual-VoLTE dual-pass.