I also had the same issue, when I filled my spouse's DS 260 form, but luckily I noticed at first instance and filled again.gotquestions12
That page has problem indeed. I personally had that issue and I've heard the same story from other people.
Lucky I noticed that answers disappeared before I signed the form.
I think you should ask KCC to unlock the DS260, add answers again and submit.
But for me it happened only once (list of country travel disappeared), and never happened again.
But for my ds 260, I never experienced such, I think not all the ds260's having that issue.