CPU led error on a Tomahawk sound like a CPU failure, especially if it works well with a 3000 series and have the bios to support 5000 series ... Try a cmos reset first (you never know, it may help indeed), but I wouldn't hold my breath on that
Had the same led lighting up on mine (x570 Tomahawk and 5950x) ... CPU is now under RMA
If you got it from a reseller, try getting him to change it (might be faster then AMD's RMA), else you should open a ticket with AMD to start your RMA process ...