Does Synfig have an autosave feature? If not, there needs to be one! If Synfig crashes randomly or my battery dies (and I have a bad habit of not saving regularly so that I don’t lose too much or all my progress suddenly), I’ll either get sent too far back to catch up or lose everything and have to start from square one. (Also, make sure the autosave feature is in the “File” menu or the main “Options” menu from the “Canvas” menu to make it easy to get to.)
Synfig does have autosave feature
Although it appears to be installed with autosave switched on, I have found that sometimes, especially in the Windows version, I have to switch it off and then on again for it to actually start working.