- make sure JGit is available as Git tool in your setup
- create a single branch pipeline from https://github.com/zbynek/submodule-grandparent , branch "main"
- add "advanced submodule behaviors" and either left all checkboxes blank or check only recursive checkout
- command line git is used and build works
- JGit is used and build fails
Known workarounds: check some of the other checkboxes or fill in some fields (use parent credentials, max number of threads, ...)
Notes: the code handles these options one by one source, it may be better to simply disable JGit when the submodule block is present.