Problem with Paper: disappearing papers

I started to use Paper yesterday (on Windows PC and Android phone). I have three papers. After creating paper 3 (on Android phone) I suddenly noticed paper 1 (created in Windows PC) suddenly had disappeared from the list within Paper. I could still see it in Dropbox itself but when I doubleclicked on it the Paper app opened but it didn't open the paper. (Which shocked me because it took me a few hours to create paper 1...!)

I decided to search for paper 1 using the Paper search option and luckily, to my relief, paper 1 was found and I could even open it! But it still didn't show up in the Paper list and clicking on it in Dropbox also still didn't work.

I decided to make a copy of paper 1 in Dropbox itself (in another folder): that succeeded and clicking on that copy also opened it in Paper directly! Victory! So I deleted the original paper 1.

Just a few minutes later, after editing one of the papers, paper 3 had disappeared from the list in Paper. Same story: it still was there in Dropbox but doubleclicking only opened the Paper app and not the document. Also this document could be 'saved' by searching for it. And this time it also showed up in the Paper list. However, I still can't open in from within Dropbox and even more odd... after changing the title of paper 3 into something else (within Paper) the new name showed up in Paper but Dropbox still shows the old name... no matter what I do.

I also notice that within Paper 2 documents show when they were last viewed but 1 document (paper 1) keeps on showing a time from yesterday, as if I didn't open it.

Anyway... the information in these 3 documents is very important but I have to say I don't really trust Paper at this moment... Anyone knows what's going on with these papers suddenly disappearing and apparently not syncing well?