BE550 and BE9300 are two different boxes. BE550 firmware won't work on it. https://www.tp-link.com/us/support/download/archer-be9300/

Same issue with BE550 and 1.0.8 here as well. Downgrading to 1.0.7 appears to revert to previous behavior that allows for saving with OFDMA+MU-MIMO enabled. I did not experience any other issues with...