This definitely should not be happening!
When you say a project has disappeared: what exactly do you mean by that? Does that mean that you open Tropy and the project does not open automatically? Or does that mean that the project file is not there anymore? Or that that the project file is there, but the contents of the project are different?
When you open Tropy and the previous project does not open automatically this can have multiple reasons, many of which are totally benign. If this is the case, what happens if you open the project file in question explicitly? (E.g., by using
File -> Open from the menu.)
If the project file has disappeared I’m fairly certain the problem might lie outside of Tropy. Tropy never outright deletes a project file; it’s possible to replace a project file (and so there is a slight possibility that the file gets deleted during that process, but it’s more likely something else is deleting the file).
If the project file is there, but the contents are not, then it’s possible that you were inadvertently overwriting existing projects when creating new ones. Tropy should ask for confirmation before this happens – if you struck an issue that makes this happen without confirmation it would be critical to fix this. Basically, when you create a new project, Tropy you can give it a name and Tropy should convert that name to a file name (which is not taken yet, i.e., if you create multiple projects with the same name, Tropy should create different files). However, you can also tell Tropy which file to use before creating the project. If you pick a file that already exists in that process Tropy should ask for confirmation, because the original file will be replaced when you create the new project.
Depending on which of these scenarios matches your issue we can try to debug this in different ways. For all of them, however, it will be helpful for you to carefully note the location (and existence) of the project file and, if you notice any errors, to open the log folder and save the
tropy.log file (which might contain clues as to what went wrong.