Character has disappeard

Character has disappeard

I have an ongoing note which I update regularly.  Created over 7 months ago.  I recently was going to update it in the Android App (which I was sure I had done numerous times), when I noticed that every word in the entire document is missing the letter 'e'.
I checked other documents with the Android App and they appeared correct.  Assuming it was a bug in the Android App, I then logged on from my computer and see that they are actually missing.
I thought that perhaps I did a search and replace by accident, so i looked here to see how I may have done it, and notice that there is no search and replace feature.
Any idea what may have caused this?  I know this sounds ridiculous, but if it's not possible to search and replace in the app then there is nothing that I could have done to remove the letter 'e'.  Which then concerns me with the integrety of my other documents.