As we will show later in the paper, these convergence issues of DM21 cannot be resolved by standard SCF setting adjustments. We demonstrate this by going beyond an SCF procedure and employing a direct orbital optimization algorithm for DM21 cases that could not converge with our SCF protocol. Even then, the DM21 convergence still fails, underscoring a fundamental limitation in DM21's ability to extrapolate to transition metals. In addition to testing DM21's accuracy for TMCs, we analyze SCF convergence failures for specific TMC systems, compare DFT features of TM molecules against their main-group counterparts (e.g., CrO vs. CaO/CO), and demonstrate that the former can be easily missed when training machine-learned functionals.