Well, bah humbug. Took the cards out and reseated them. Have to say it's absolutely mint inside - I guess that what happens when you have no fans sucking in dust. Alas, this did not fix the issues. So now it's off to Marc for a proper fixing. Then I shall be selling it.

Cave: Trinnov Altitude CI-8; Oppo 203 Vanity HD; 6xDSP5k, DSP5kC, D1500; Sony Z9D, PS5 Pro; Apple TV 4K
Living: Wiim Pro; Rega Planar 1+; 2xDSP5k
Master: Wiim Pro; 2xDSP3100
Kitchen: Bluesound Flex stereo pair / Amazon Echo Studio
Deck: Wiim Mini; Random Chinese Class D; Cambridge Soundworks Outdoor 52s; Polk Sub;
Garage: Wiim Pro; 2x5k