Perhaps I'm the only one confused, but from what you've posted so far ...
- I can't tell if you've got log problems in both ASE 15.5 ('source') and ASE 15.7 ('target') or just ASE 15.7
- from a replication perspective I can't tell if you've got log problems in your PDB ('source') and/or the RDB ('target')
- I can't tell if your log is 80% full or 100% full when you successfully issue 'dump tran w/ no_log' [I would expect all 'dump tran' options to clear the log @ 80% full, while 'dump tran w/no_log' would be your only option if the log is at/near 100% full]
- I can't tell from your commentary which databases have records in syslogshold and which of said records are valid or invalid [I don't care about 'dbcc gettrunc', I only need to know if a database has a record in syslogshold with name = '$replication_truncation_point']
It would probably help if you start over from scratch describing your issue.
1 - Are you having problems with the log filling up in ASE 15.5? [yes or no]
2 - Are you having problems with the log filling up in ASE 15.7? [yes or no]
3 - For each database where the log is filling up:
3a - if the database is a primary database (PDB) in a replication configuration, is there a matching record in syslogshold?
3b - if the database is a replicate database (RDB) in a replication configuration, is there a matching record in syslogshold? [if there is a record in syslogshold, it should *not* be there; remove with 'dbcc settrunc(ltm,ignore)'; keep in mind that if the database is both a PDB and a RDB then the record needs to exist in syslogshold]
3c - if the database is not part of a replication configuration, is there a matching record in syslogshold? [if there is a record in syslogshold, it should *not* be there; remove with 'dbcc settrunc(ltm,ignore)']
3d - when the log is 80% full (or any appreciable amount below 100% full), does 'dump tran /to_file' or 'dump tran w/ truncate_only' clear the log?
3e - Is the log 80% full, or (near) 100% full, when you say that 'dump tran w/no_log' is the only command that clears the log?
3f - Once you've issued 'dump tran w/no_log', does log space usage drop back to/near 0%? alternatively, what does 'sp_helpsegment logsegment' show after running 'dump tran w/no_log'