Yaw damper generally is to provide a moderating influence on Dutch Roll tendencies.
Dutch Roll gets worse with increasing altitude, ergo, no Y/D = height limit if the DR problems warrant.
Similar limitations can exist for aircraft with additional fins included as certification flight test fixes for directional stability.
For instance, having a copy of the Super King Air POH and MMEL on the desk at the moment, that Type runs to FL 350 per the TC but, with Y/D U/S the limit is A050. With Raisbeck mod per STC SA5151NM (aft body strakes - couple of fixed fins under the tail) the A050 limit increases to FL 190. If, for instance, one demoded the aircraft, say, for damage recovery to base considerations, the basic limit of A050 would then apply for the ferry recovery.