Text Edit Files not fully opening

I recently noticed that two Text Edit files (both rtf files) seemed to have been cut in half. One, for example, is a long list of movies I might want to see, and suddenly the last entry was one I entered over a year ago. I tried opening and reopening and nothing helped. I had not been using Time Machine, so my only backup was in the cloud and thus was as "damaged" as the original. However, yesterday the file suddenly seemed to have been repaired. What I saw happen was that, when I got to where it had been ending, the scroll bar no longer appeared to be at the end and, scrolling down, all that had been "lost" was found. However, I am having the same problem with another Test Edit document. In this case, only the top half of the last visible line of the file can be seen, and a good chunk of the document seems to be gone. I recently updated to High Sierra. I can't be entirely sure the problem started with the update, but that is possible. Anyone have any idea what's going on?