I'm pretty sure that command is broken because it says "0". Also, my witch farm still works which would imply the seed is still the same. Or, at least it's extremely unlikely that another witch farm happened to generate in the same spot.
Slime chunks are broken as well. Experiencing the same things as you, witch farm works, guardian farms do not.
How can I tell?
Yep. My guardian farm no longer works.
I'm pretty sure that command is broken because it says "0". Also, my witch farm still works which would imply the seed is still the same. Or, at least it's extremely unlikely that another witch farm happened to generate in the same spot.