@pob
Yes, had a similar experience on the 3 lines I monitor, 2 X Plusnet 40/10 and a BT 80/20, monitored 24/7 with RPi's running DSLStats, same exchange, different DSLAM's.
Happened on 10/12/19 due to re-synch's caused by DSLAM outage which appeared to be a scheduled software upgrade.
The product on all 3 modem's was higher than expected DS & US synch rates with associated lower SNRM's.
Was advised by forum patrons that this was likely due to my monitored modem's synch'ing faster than most on their respective DSLAM's so minimising any potential cross talk factor and producing higher synch rates.
As CarlT advises, your line will likely return to normal expectation stat's on the next re-synch, my lines certainly did.
The lines did maintain synch for quite a long time and the eventual re-synch's were not DLM instigated.