I pulled my SD out and see that it has about a dozen files with junk names on it. These were accumulated after two weeks of operation. I think they were all junk and could not be read or erased. The files I wanted were all there and OK.
I had a similar thing before, and about the same number of files, but this was after a year or so of continuous operation. That time, some files were recoverable by renaming them.
If I run Arduino, the junk files are not made straight away, i.e. everything seems normal and, as I said, the files I need are made and are kosher..
Does this sound familiar with anybody.