The code here:
https://github.com/BoldGrid/library/blob/master/src/Library/Start.php#L181-L187
doesn't work properly to determine the actual WordPress path when WordPress Core is installed in an alternative place. This causes major plugin broken UI issues as CSS & JS assets can't be loaded properly. This should be using WordPress Core methods for determining paths & URLs.
The issue was originally reported here: BoldGrid/boldgrid-backup#546