This solution worked to get past the maintenance message that took the site down. Thank you Leonid!

Hi all!

At present, a potential resolution to this predicament entails accessing the CPanel file manager, navigating to the UNA site directory, and renaming the .bx_maintenance file to 1.bx_maintenance. Subsequently, proceed to the Studio section, select Apps Market, and proceed to the Updates area to finalize the upgrade process for all installed modules.