Usually the commit hash of the monero submodule shouldn't matter for building since it is set to an appropriate target at the start of building, but the current monero commit hash 782a9f6 has a problem in its miniupnp submodule because it points to the now obsolete repo under monero-project. Git refuses to checkout to master because it references a commit hash in the official miniupnp repo (which doesn't exist in the repo under monero-project).
Usually the commit hash of the monero submodule shouldn't matter for building since it is set to an appropriate target at the start of building, but the current monero commit hash 782a9f6 has a problem in its miniupnp submodule because it points to the now obsolete repo under monero-project. Git refuses to checkout to master because it references a commit hash in the official miniupnp repo (which doesn't exist in the repo under monero-project).