### Please describe the problem.

"git status" returns a list of almost all files in the annex (located on a FAT32 device) with these messages:

    git-annex: git status will show music/a.flac to be modified, since content availability has changed and git-annex was unable to update the index. This is only a cosmetic problem affecting git status; git add, git commit, etc won't be affected. To fix the git status display, you can run: git update-index -q --refresh music/a.flac
    ... (a lot of similar messages for +30000 files)

and then a new list of messages:

    ...
    git-annex: thread blocked indefinitely in an MVar operation
    error: external filter 'git-annex smudge --clean %f' failed 1
    error: external filter 'git-annex smudge --clean %f' failed
    git-annex: thread blocked indefinitely in an MVar operation
    error: external filter 'git-annex smudge --clean %f' failed 1
    error: external filter 'git-annex smudge --clean %f' failed
    ...
    refresh index:  81% (30495/37394)



### What steps will reproduce the problem?


### What version of git-annex are you using? On what operating system?

debian sid, git-annex version: 7.20190129


### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log


# End of transcript or log.
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)


