Target SNR is one of the configurable attributes of the DLM and a profile that your ISP should be able to request BTw to change.
Most ISPs are able to do this sucessfully for their users, but it would seem that some CS departments of ISPs have more problems in processing this than others. Whether this is down to a lack of understanding of how the system works, or some other complication I dont know.
In theory the DLM should look at reducing your Target SNR after a period of stability - but there appears to be no BTw guideline of just how long this period is. Some have rumoured a month, but it could be much longer than this, and Ive seen users report no change after much longer than this, therefore its easier if (after a problem has been resolved) you can request this change via your ISP.
There's not just you evs thats having this problem, Ive had correspondence via other means of people being in the same boat, with their ISPs saying such things as the user needs to contact BTw, or it will change after 3/10 days - obviously both of which are false.
The problem here is sometimes getting through to the right person in CS support who understands what needs to be done, and all we as end-users can do about this, is keep on at our ISPs