Love MainWP - just trying to help with feedback on what I am seeing/experiencing with the 4.3 Beta.
Not sure if this is an issue on my end or with 4.3 Beta - after updating I get this message for each child site with a RED X next to it:
WP Config debugging is disabled
Checks if WP Config debugging is disabled
Technically it’s a grey X with red around it. 
You’re not the only one. There are even a couple of topics about this. Almost every site I manage has this, while WP_DEBUG is definitely set to ‘false’. So this check is probably broken and we’re waiting for more details about how this is checked.
The problem has been fixed.
I just got an update from the dev team and confirmed. Will be included in the official release.