I'm new to SolidWorks 2018 (and am on SP1), but I have been using the Design Checker in 2015 to standardize sheet formats (among other things). I didn't use the intervening SolidWorks versions, so I'm not sure if this behavior is new to 2018, but when the Design Checker corrects the sheet format, it hides the sheet format -- it appears to uncheck the "Display sheet format" in the Sheet Properties.
To make it reappear, I just have to go back in and check the "Display sheet format". The behavior doesn't seem to be available in the GUI for the Design Check Builder.
Can anyone confirm, or offer a solution?
Thanks for your time!