Question on textconv

I experienced a change in how textconv works since about 2.50 and it is hard to get past. I would appreciate advice:

When I define an external binary textconv, roughly like:

.gitattributes: simple binary diff=enscr

.gitconfig
[diff "enscr"]
        textconv = run -debug ../../enscribe-conv --verbose
        binary = true

The supplied file going to the textconv program looks like /tmp/git-blob-GFtIhK/simple and is always empty regardless of the file contents.

When there is only one file named simple in the repository I can find it, but otherwise any ambiguity in the name makes textconv processing impractical. Somewhere prior to this I was supplied with the actual file in the working index instead of a temp file.

Am I missing something?

Thanks, Randall