This is just a reminder post: keep your valuable worlds backed up!
The easiest way to do it is to upload them to Dropbox. Android users can also upload to SD card (or internal storage), which does not require setting up an online account.
I put a lot of work in the save system to make it resilient. On top of that it keeps 2 copies of the most important data. Once the worst happens, the game tries its best to recover corrupt saves.
However, once in a while a bad crash happens or your battery runs out and the game dies in the middle of writing something important. Survivalcraft autosaves every 20 seconds, so the risk is real. If you’ve worked for a long time on something, back it up, or you’re tempting the fates.