@Richard_Dower
Hey, that was really good of you to post the root cause - Many lesser men would have just silently slipped into the interwebs.
Kudo's to you for sharing what you discovered and hopefully it will help someone.
Other systems in addition to rig in the profile specs:
Aorus Master x570, 3950X, 32GB GSkill c16 @3800, Sabrent PCIe4 1TB, Sabrent 1TB, 860Evo 1TB, 2080 Super, HX1200i, Celsius S36, Define S2, pg348q
Aorus Master x570, 3900X, 32GB GSkill c16 @3800, Sabrent PCIe4 1TB, 860Evo 1TB, 5700XT, HX1000i, H150i Pro, Obsidian 500D, LG32GK650F-B
MEG x570 Unify, 3800X, 32GB GSkill c16 @3800, Sabrent PCIe4 1TB, 860Evo 1TB, GTX1080Ti, SSR-850PD, Celsius S36, Define R6, u3415w