I can reproduce the issue by checking out this repo and running vim -u vimrc. I get the following error repeatedly:

E475: Invalid argument: 0

I've attached a log for help debugging.

vim.log

I did some debugging already and added some echom commands to see where the failure is occurring. It looks like it's getting the results of the curl command fetching the branch name in the first Blink command. I added an echom of the full curl command, which appears to be the location of the error, and the curl command appears fine and executes just fine when I run it outside of vim or via :!.