It happens to me too when my wi-fi gets overwhelmed. I think the connection is the problem. The client doesn't get messages from server. But my friend Rantisky the other day couldn't see his BD pets and they were all right there. And we were carrying on a conversation so I know he was connected. Then according to him I disappeared, the mob we were farming disappeared and my pets disappeared. So he relogged. But I'm sure it's network related.
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"Once more into the fray. Into the last good fight I’ll ever know. Live and die on this day. Live and die on this day."
- The Hunter's Poem