The MAXDELAY constraint used in the design might not be connected, or they are on a different clock.
Diamond STA won't analysis on different clock domains unless they are related by clkskewdiff
For Example, if two cells are in different clock domains:
MAXDELAY FROM CELL "A" TO CELL "B" 18 ns;
CLKSKEWDIFF CLKPORT "clk1" CLKPORT "clk2" 0 ns;
For Example, if two cells are in the same clock domain:
MAXDELAY FROM CELL "A" TO CELL "B" 18 ns;