Upgrade, using Softaculous, from 1.31.0 to 1.32.0.
The Site died with following error. "undefined option: 'ResourceLoaderLESSVars'"
Added "$wgResourceLoaderLESSVars = false;" to the end of LocalSettings.php and error disappeared.
Topic on Extension talk:MobileFrontend/Flow
You should upgrade extensions when you upgrade core. It sounds like you're running MobileFrontend older than your MW Core version