If you have not yet, try restarting all your network gear just to see if it helps. 65mbs indicates 2.4ghz which can get oversaturated by other houses WiFi. It might have more cross channel interference from a neighbouring system. The rate it says is rarely what it is either that’s a max transmission rate not actual. WiFi is up and down all the time and Roon as I said is uncompressed and can just tip it over if this already borderline as pcm is much larger than flac. Given it was fine a few days ago and your other systems are ok it can often point to WiFi interference. WiFi isn’t the same minute to minute let alone day or day and now a neighbouring WiF system might have changed to be on the same channel.as yours.