I have a friend with similar setup: Roon Core, QNAP and DSM as streamer. He also have similar problems with strange clusters of dropouts.
We did a longtime test with my DS/1 as streamer, but everything else stays the same. He could not notice any dropouts using the DS/1. Switching back to to the DSM and the droputs comes back.
Linn asks for a verification test using Kazoo for the DSM which gives no dropouts whatsoever. Both Tidal and own library tested.