Cracking is the chronic issue with most tennis courts, particularly ones made of asphalt.
Structural cracks which run the depth of the slab typically return in the form of hairline cracks at first and continue to widen over time due to the natural expansion and contraction of the slab from temperature variances.
Fix - Grind level any displacement, fill and resurface.
Hairline cracks are small surface cracks not yet structural.
Fix - Properly fill and resurface.