I've had this issue myself. I looked all around where I killed it, and I could not find it. For your information, I was playing with a friend, but we weren't on Realms, and at one point the chunks were unloaded and I changed the difficulty when I died and realized I wasn't exactly ready to defeat the wither. I'll try to reproduce this, I just have to get more wither skeleton skulls soon.
Julian Aristizabal
I've had this issue myself. I looked all around where I killed it, and I could not find it. For your information, I was playing with a friend, but we weren't on Realms, and at one point the chunks were unloaded and I changed the difficulty when I died and realized I wasn't exactly ready to defeat the wither. I'll try to reproduce this, I just have to get more wither skeleton skulls soon.
Edit: I'm on the latest version, 1.16.201