Parts are mysteriously missing

When I exited the project while offline to work on another project, and returned to the project again to load it, the part I spent two days working on was inexplicably missing. No matter how I looked for it, it just disappeared. This made me very sad. Collapse, which forced me to start spending time on this project again. It really wasted a lot of my time to produce products. Please pay attention to this issue, please.