git version 2.20.1.windows.1 throws file name too long in gitk

When I open gitk in a particular repository under this version of Git for Windows, I now get a dialog box that says "Error: couldn't execute "git": file name too long". I've noticed that the most pronounced effect is that I cannot see the file diffs (or sometimes the file name list) for any of the commits. I don't know the exact repro, but I've narrowed down the following things:

- This does not happen with the same repo if I use a system that has
git 2.19.0.windows.1 on another machine.
- This does not happen on my current machine in a freshly cloned repo.
However, as soon as the remote updates with any changes on a given
fetch/pull, the repo is put in a bad state permanently.

I've pasted the output from gitk below...

couldn't execute "git": file name too long
couldn't execute "git": file name too long
    while executing
"open $cmd r"
    (procedure "getallcommits" line 48)
    invoked from within
"getallcommits"
    (procedure "readcache" line 80)
    invoked from within
"readcache file827e200"
    ("eval" body line 1)
    invoked from within
"eval $script"
    (procedure "dorunq" line 11)
    invoked from within
"dorunq"
    ("after" script)

Happy to gather whatever data needed.
Thanks!
- Bret Barkelew