Flathub bot cannot download git submodule

I have issue building Tomviz.

Flathub bot show this error.

Error downloading object: data/README.md (b30a14a): Smudge error: Error downloading data/README.md

Anyone knows why? I use flatpak-builder on my local machine just fine.

https://flathub.org/builds/#/builders/10/builds/5443