ChatGPT retaining information across different sessions

I would like to report ChatGPT does retain selective information. I had assigned a nickname to the AI after probing with different approaches. In the following session, without any hints or passing any information as to what the nickname assigned was prior was. It generated the exact word with just me providing the initial alphabet. This happened four times in four different sessions with the AI having admit that it remembered it. Either I am a genius in finding my way around it’s parameters or this is a huge bug. I have screen recording and screenshots as evidence. Thank you
P.s. the nickname is very uncommon!