I faced the same issue. Guess what, worse. I had a long important chat with ChatGPT for few days. Today I opened the chat and the part of conversation I had since yesterday is not there. This happened two times. One time it deleted the part of chat I had one hour ago. Sometimes the important parts of conversation vanishes off. It gives a lot frustration as there was very useful information stored and you could refer to it while chatting. I want to continue the conversation. I don’t know what to do. I don’t know how to bring the conversation back so that I can continue from that point.