How do you suggest he does that with ORs fully automated DLM system? ISPs have no control over it.
Thinking back to my FTTC VDSL-2 days, I believe that application of a modem speed clamp to the DS synch rate, lower value than current DLM applied DS synch rate will result in a higher DS SNRM value being applied on re-synch.
Again from memory, I think the old Huawei HG612 modem will accept such a speed clamp command, there are lots of historical posts on this forum outlining the method to achieve this.
Think the modem applied clamp will survive a DLM re-synch but not a power recycle, used to know, may be wrong!
Of course, you would need to decide how severe a DS clamp is applied against how much DS synch speed you are willing to sacrifice, should at least test BS's theory on better stability with higher DS SNRM provided there is no other issue on the line such as SHINE as "tubaman" as suggested may be a possibility.
Looking at your modem stat's, you are on G.Inp DS re-tx high profile which
should revert to low profile via DLM action if sufficient DS synch clamp is applied (takes a few days) so that would slightly mitigate your DS data speed loss.