Originally Posted by -One-

I also experienced this problem. Exactly as you described. Saved a rudimentary version to test out the first couple of encounters. Finished up working on it later and played it through to the end. Noticed some dialogue errors so I backed out to edit but when I tried to replay it I got an internal server error. Relaunched, and still got the internal error so I deleted my foundry character & created a new one. The mission was still there but it had reverted back to the original save. The entire second half of my mission was gone.

It is a frustrating issue but this is what Beta is for. Just try to identify what may be causing it and try to reproduce it for a comprehensive bug report. The Devs need that info if they're going to hammer it out.