We never use Latium rule checking.
Are you routing with DRC in prevent mode or not?
Layout is using code from the Router for Latium error checks. Latium is the technology Router is based on. So Router DRC IS Latium DRC.
Enable "Show guard bands on object" to see the spacing when routing and editing.
Use the Stretch command to edit and move diff pairs around. Using a smaller grid when you do this is usually helpful. You can visibly see any spacing error when selecting any trace with guard bands on. Always keep DRC on when doing this.
Design Verification has a specific setting for Diff Pair spacing with adjustable error conditions.