Git status gives me error message: bad index file sha1 signature

In my git repository, I did utf-8 convert many files, but only below the .git directory, so the .git directory was not affected. Before this conversion, I created a new testing branch, but now I can no longer use my repo, I can not return to the wizard. When I do this:

git status 

or any other git command that I get:

error: bad index file sha1 signature 
fatal: index file corrupt 
fatal: 'git status --porcelain' failed in submodule core/kimai-mobile

I searched about it and found a command:

rm -f .git/index 

and after that:

git reset

but it did not help. I do not understand what is wrong. Then I removed the "submodule" core / kimai-mobile, and I was able to use it again!

git , . , , "" .

:)

, git , ?

"" git:

.gitignore

...
# kimai mobile
kimai-mobile
...