iPhone 15 keeps asking for sim pincode without restart

I have a work iPhone 15 plus running iOS 18.4.1, which I mostly use for testing and receiving notifications for emails.

Since I don't actively use it every day, I often find that when I pick it up, the SIM card has been locked and I need to re-enter the PIN code.

This means that it hasn't been able to receive notifications, and I have no idea how long it's been locked.

I'm not sure if this is a power-saving or security feature, but I'd like to disable it so that I only need to enter the SIM PIN code when I restart the phone.