When some of them are determinately stuck.

1. First, shut down any running simulators:

bashCopyxcrun simctl shutdown all

2. Then, delete all devices:

bashCopyxcrun simctl delete all

3. Reset the simulator completely, you can use:

bashCopyxcrun simctl erase all

4. You may need to kill the process before your list is cleared:

killall -9 com.apple.CoreSimulator.CoreSimulatorService

Verify with:

bashCopyxcrun simctl list

Also you may need to restart your devices before things took effect.