In Replication Server 15.7 or later, the subscription length limit is increased to 255 characters from the previous limit of 30 characters in rs_subscriptions.
The subname column in the rs_subscriptions system table changed from varchar(30) to varchar(255).
See Replication Server Reference Manual> Replication Server System Tables >rs_subscriptions.
In a mixed-version replication environment, you must ensure that your replicate Replication Server and your primary Replication Server version are both 15.7 or later.