You may get an out of date symbol if you have assembled component B & component C to Partfile A, and you have mated B & C in A(Mating condition is between B & C).If you suppress the B & C components using suppress by expression. You will get out of date symbol. This cannot be removed.
Only work around to remove the out of date symbol is to mate the component B to A and suppress Component B. Similarly for component C.
Regards,
Karthik J