Some of 8 contacts lenses might short the battery in some case while hot swapping.
If it happens, the Z Type batteries might got locked. To unlock it is easy: put the locked battery into wall charger and charge it for at least 10 seconds, then it would be back.
But, the old FW50 batteries do not have protection circuit, the worst situation is it might brick the camera.
To avoid this, please make sure your camera is off when you try to swap the lens.
The lens will be moved to infinity after the system ready to power off, so please do not swap lens before they are at other position.
Or, you can pull out the battery out, this is the safest way.
And, the 3rd way is rotate the adapter(not lens), separate the adapter and camera first, then you’re good to go.