Could be a hardware issue with the Accuphase. Odds are the DAC external and internal have high analog signal levels. Something could be wrong with the Accuphase that clears up once it heats up. It certainly would not be unheard of.
Given that attenuating the signal in Roon seems to make the issue better, this seems like a logical conclusion. That will reduce the analog signal level entering the amp.
Reducing the volume via the amp may not alleviate the problem depending on where the problem is.
If it happens on both channels, to me, it sounds like an issue with a power supply supplying the input circuitry. If the voltage is low, it will clip / distort the input. Bad solder joints can also resolve via soldering, or movement, only to come back again.