keep the vehicle1 in its original state while controlling vehicle 2

Expected Behavior

I want to control multiple drones separately in QGC.

Current Behavior

When connecting two drones like vehicle 1 and 2, control one to fly, and the other will automatically enter the return landing mode. But I just want the other drone to do what it needs to do or hover

Steps to Reproduce:

I conducted multi vehicles（vehicle 1 and 2） simulations in jmavsim
Open the QGC, connect to the two vehicles successfully
Press the takeoff button on the left side of QGC to make vehicle 1 takeoff
Press the switch button in the upper right corner of the screen to switch to vehicle 2
Similarly, let vehicle 2 takeoff
At that moment, I noticed that vehicle1 seemed to have lost its connection and entered landing mode automatically. I don't know why this is happening.

System Information

When posting bug reports, include the following information

Operating System: Ubuntu
QGC Daily Build: version 4.2.9

Detailed Description

When I took off vehicle 2, vehicle 1 seemed to lose connection and landed automatically I wonder if switching vehicles through the button in the upper right corner will cause a loss of connection ？

I just want to keep the vehicle1 in its original state while controlling vehicle 2. Has anyone encountered this kind of problem before? How should I solve it. Please help! Thank you very much!!

Log Files and Screenshots

Screenshots of Initial simulation: QGC successfully connected to the vehicles
Screenshots of Error condition: We can see from the right side of the screenshot that vehicle 2 is taking off but vehicle 1 is returning to land automatically. This is where I don't understand.

mavlink / qgroundcontrol