Hello,
The issue is most likely your failover configuration.
I can see that you have failover enabled on SIM1, however, if you only need to switch between different SIM cards on certain conditions, SIM Switch needs to be used. It can be configured in the Network → Mobile → SIM Switch menu.
For the failover, if you will not be using wired WAN or wireless STA mode, I'd recommend disabling failover completely (just disable all interfaces in the Failover menu).
When configuring SIM Switch, remember to configure the secondary SIM card to switch back to the primary under the specified conditions.
Let me know if this helps!
Best regards,
DaumantasG