Sorry to hear about the issues you’ve encountered. Unfortunately there is not likely to be any other way to recover your information if you have gone through the steps in our recovery guide, which it sounds like you have. There have been problems in past versions of Pencil2D in particular with frames being wiped like you describe, but most of those seem to have been fixed by improvements in the latest version. The only file wipe cause I am aware of that still applies to v0.7.0 is under quite specific circumstances when copying and pasting frames on the timeline of a large project. This will be fixed in the next version of Pencil2D, but I honestly don’t recall any user reports of file wipes caused by this yet.
What I would recommend doing for future animations is first make sure you are using the latest version of Pencil2D. You can check your version by going to Help > About in the top menu, it should say that you are using 0.7.0 in the popup dialog. If it is lower than that version, please upgrade. Once you are up to date, the only other thing I can recommend to avoid this situation in the future is to make frequent backups of your project. The unfortunate reality is that projects on rare occasion become corrupted. While we try our best to make Pencil2D reliable, issues like this have proven challenging to reproduce or locate the cause of, and certain scenarios such as hardware issues or power outages will always remain a possible cause of corruption no matter what we do. By making copies of your project as you make progress, you can reduce the amount of work you risk losing in the case something goes wrong.