While indicators both those things can happen on a connection through the normal activity of the DLM
This is very much the case - The old style of DLM intervention (FEC+interleaving) would typically drop speeds and add latency.
The whole point of G.INP, as a new style of DLM intervention, is that it reduces errors without dropping speed or increasing latency.
My line was synced at 80/20, and only hitting about 2 ES's per hour - well under any intervention threshold for the old-style DLM.
It has had G.INP activated, which has left the sync speeds alone, has made no appreciable difference to latency (I see bigger differences by gateway hopping, so it is hard to see the actual impact of G.INP), and it has dropped my error rate to zero.
At the same time, my attainable rate rose by 6Mbps down, 2Mbps up.
However...
We have seen G.INP activation cause drops in speed and increases in latency - but it appears to be mostly (perhaps entirely) down to using a modem that has not been upgraded with G.INP-capable firmware.