A recent update of my conda environment for psi4 as well as libint from v. 2.8 → 2.9.0 has solved this error and I am able to successfully optimize my structure w/o any problems. Working on benchmarking the results with some prior calculations I did in another comp chem suite.
Thank you all for the points/references about density fitting approxs. & the use of more modern basis sets. We tend to be a little stuck in our ways in terms of method/basis set choice based on literature precedents, especially when it comes to DFT calculations to support mechanistic pathways for organic syntheses. Not a lot of studies out there are willing to put in the work to benchmark newer methods but hopefully we can start to shift the paradigm there.
Cheers!
b